Japan IMHO would get everything they got IOTL because Germany can't take it back; maybe Japan would pay a pittance for it at the peace treaty to smooth things over. Otherwise I think that Japan and Britain would remain allied because Britain needs allies after losing a war. So Japan pretty much acts per OTL except with British backing. I'm not sure there would be a naval treaty post war though.
Germany get payback and just plain paid by helping China out in the 1920s and 30s. Germany would want an Asian market and ally, so by having no colonies in Asia or colonial interests in China, Germany would be China's perfect ally; IOTL instead of breaking that for an alliance with Japan, China becomes Germany's proxy in Asia, probably with a significant Condor Legion plus ground contingent expeditionary force to help build up China. It would be a 'Flying Tigers' with Germans instead of Americans.
Japan though probably isn't embargoed thanks to British influence, or at least through British underhandedness in getting around the US organized embargo (I doubt the US and Britain would be very close after TTL WW1 without US entry). I think the Dutch would be more in the German orbit, so we could see the Island Nations team up against the world in a sense, as Britain helps Japan to keep her away from British interests in Asia, while the US and Germany organize an embargo on Japan, while helping her fight Japan. If anything the US and Germany could end up getting closer thanks to the China issue. A classic 'enemy of my enemy is my friend' scenario.
I am very dubious about the idea that Germany would let its Pacific colonies go - as mentioned before, they were one of the few parts of the German Empire that brought in any money. And keep in mind the racism of the era - I very much doubt the Germans would be willing to take the prestige hit of letting some bunch of yellow monkeys occupy one of the best bits of their empire when a few of the Kaiser's battleships would send them running with their tails between their legs (as the Germans are likely to see it). It took Pearl Harbour, Singapore, Burma, Malasia, the Philippines, DEI campaign and the Japanese post-war economic miracle to break Western racism with regards to the Japanese. Also compare the situation of the French in Indochina after WW2 - even after WW2 proved that the French couldn't hold the place - they still spent enormous amounts of blood and treasure trying to retain the colony. I see German Pacific as a similar case for the German high command. They know the islands aren't very defensible, but on the other hand, letting the Japanese walk all over them is an insult to German honour and those islands are THEIRS darnit... Also, the navy are likely to be keen to actually USE their shiny battleships and thus justify funding for the next generation of battleships.
And I think the Germans would have a good chance in a fight with Japan - Japan won against Russia by the skin of their teeth. If the Tsar had been a bit more stubborn, Russia probably would have won by default, as Japan went bankrupt. Also, Japan got really lucky on both land and sea. It isn't too likely that the Japanese get another run of luck like that. Germany isn't Russia, they have a formidable fleet, with good sailors, good officers and some of the most modern ships afloat. So long as the Germans can GET the fleet to the Pacific (I think they have the logistical capacity, but I might be wrong), I think they will have the advantage over the Japanese fleet, which at this point, does not have so many modern battleships.
I don't think Britain could do anything to stop the US from embargoing Japan if Japan did as OTL and went after China. Nor do I think Britain would WANT to stop an embargo in such a situation. Britain had significant interests in China, and like the US, liked China being whole and open to trade. China was an important trade partner for Britain and will be even more important in this TL due to the importance of solidifying the country's finances in order to better oppose Germany. (China was an important trade partner due to Britain's trade with China running a surplus.)
And OTL, the British did try to keep the alliance with Japan alive for as long as they could. The problem was that the British didn't want to get caught up in a war between Japan and the US. If forced to choose between keeping Japan happy or the US happy, the British are going to keep the US happy, even if the US are a grumpily Anglo-phobic neutral (which was what the US was OTL when the British decided to let the alliance with Japan expire). Now if Germany wins WW1 and stays in the Pacific, there is one driver there to cause the Japanese and particularly the British to be more keen on their alliance (the common threat of Germany). On the other hand, Germany winning does nothing to change the risk of a US-Japanese naval war. And for the Japanese, the British have just proven themselves unable to defeat the Germans, I suspect Japan would thus be less attached to the alliance with Britain in this scenario. One thing that might change this is if the Japanese and Germans end up in a shooting war over the Pacific colonies - if Britain helps the Japanese the alliance may be strengthened by fire-forged friendship, but I don't see the British helping the Japanese unless they have decided to fight on themselves - and the original post was proposing that WW1 had ended somehow. To take the opposite case - the Japanese and Germans fight for the Pacific and the British, having already signed a peace treaty, stay out - well, then both the British and Japanese are going to be pissed at each-other no matter who wins the German/Japanese contest.
Germany and China are far from perfect allies. "China" in this period means Beiyang China, and a more corrupt and villainous lot of bandits are hard to imagine (literally bandits in some cases). They were also not terribly competent. The Beiyang regime didn't have much control beyond Beijing itself and the various warlord factions of the Beiyang regime were engaged in constant factional strife, occasionally turning into all out civil war. If Germany gets involved in propping the Beiyang up (which makes alot of sense on the surface, pushing Britain out of the China trade is a nice way to weaken the Brits while expanding the markets available to German industry), most likely it will suck up alot of men and money for very little profit.
Also, a German alliance has a potential downside for the Beiyang faction who allies with them as well - the concession in Shangdong. OTL China joined the allies in WW1 in return for receiving the German concession Shangdong. (The allies of course broke this promise at Versailles, where they studiously ignored the Chinese delegation, this scandal lead to a great deal of protest in China and would eventually result in the birth of the Chinese Communist Party.) If Germany insists Japan (who were occupying Shangdong at the end of WW1) return the concession to them and then keeps it, it is likely to be an issue for Chinese nationalists. Now if Germany keeps Shangdong and offers support to the Beiyang, I am betting the Beiyang regime would accept the support, they were in a constant state of penury. But it will mean yet another bunch of people upset at the supine corruptness of the Beiyang, more support for the Nationalist regime in the South, more problems for the German advisers in the country. Now the Germans might give the Chinese the concession, which would be a smart political move - it would give the Beiyang a big political boost. Giving the Beiyang the Shangdong concession outright is going to cause difficulties for German businesses in China though. The Beiyang don't really have the administrative capacity to govern the entrepot (they really were massively corrupt), so most likely if the Germans "gave" the Beiyang Shangdong, they would continue to run all the important things themselves (mainly police, courts and customs) which is going to have the Chinese nationalists (small "n" nationalists, not the Nationalists of the KMT in the South) asking barbed questions about the German concession that is a concession in all but name...
All this is assuming the Japanese give Shangdong it back to the Germans - see above discussion of the Pacific Islands - and if the Germans don't get the Shangdong concession back, that's going to make them look kinda weak to the Chinese in a "these guys are strong in Europe, but weak in Asia" way.
Also, I wouldn't bet on the US closeness - or lack of it - with Britain. The US has drivers to oppose the British and drivers to align with them - Germany winning WW1 changes those drivers - but it could change them in either direction depending on host of factors. If the US stayed out of WW1 entirely it means the interventionist faction hasn't had its fingers burnt, so we could see a much less isolationist US. On the other hand, the US could be as isolationist as OTL in the 20s and 30s. Even so, American business will still be expanding internationally and the US is likely to keep the Pacific and China as exceptions to its isolationist attitudes just as it did OTL. It is very likely that the US and Germany end up competing for business and influence around the world. This becomes more likely the worse Britain does in the 20s. Britain pre-war dominated trade with Latin America, Japan and China. If Britain is out-competed by the US and Germany and withdraws within her empire, it will be the US and Germany contending with each-other for the prizes.
Also, just as the British disgusted the Americans with their behavior in victory, the Germans are likely to disgust them also. Just as the 1920s saw the Americans get closer to the Germans in OTL, I could see the Americans getting closer to the French and the British in TTL. (Particularly the French - just as the US funneled loans into Germany to rebuild it post war, they are likely to funnel loans into France in order to rebuild it and thus keep a semblance of a balance of power in Europe.)
Worth mentioning is that Britain, as a matter of long-standing policy, has generally tried to give the Americans what they wanted (much to the ire of the Canadians when this involved giving away bits of the Canadian colonies to keep the US happy). Faced with a German Empire supreme on the Continent, Britain is going to be very keen on keeping the US as friendly as possible. If nothing else, America is a hugely important trade partner, and a trade partner that isn't under threat of being cut off by the Germans. While a series of bad accidents might drive Britain and the US into opposition, it is rather unlikely that such a string of bad luck would happen. More likely both countries maintain a friendly neutrality that is more or less distant depending on the internal politics in each.
Though a TL featuring a 3-cornered cold war between Germany, Britain and the US (and their sundry allies) would be a rather fun one.
fasquardon