The consensus seems to be that African colonies are used as bargaining chips in lieu of real concessions in Europe. I tend to look at most floated "war aims" as hyperbole, the aim might be far but the reach is what it actually is. In most scenarios I can craft Germany gets some range of her colonies returned, it takes something looking like a victory to get any gains and I really only see that coming out of Belgium and France's holdings, anything from the UK is just as much hyperbole.
I have two scenarios, one with a non-belligerent UK and the other a belligerent UK, both result in an essentially stalemated war as concerns he UK and France. In the former we do not involve Belgium and do not occupy northwest France, in the later we have the war with all the usually players. The conundrum is that for Germany to win the former scenario works best, but gives it the least leverage unless you indulge in some leniency for Germany to give her a strategic breakthrough, or in the latter you have Germany too exhausted to exploit the gains.
As much as the colonies are not that valuable in 1917-1919, I keep returning to them because they add complexity to the future and opportunity for some better fiction. Where else does Germany build its spaceport but East Africa? And why not play with Germany more at odds with Imperial Japan and rattling around in China? But I digress.
My least likely but rather favored would be limited war and no UK at war, that requires France to take German colonies and I think that limits things to Togo and Kamerun, maybe the Pacific islands and Quingdao and/or Tientsin. And if Germany can push into France at all then these can more easily be traded back and the more of France overrun the more France would offer up. Here I think you can argue for some portion of Equatorial Africa, likely not Chad at all unless you conjure Italy in the CP then it might occur to someone to link things, and maybe Dahomey. Indochina, Algeria and such sound of fantasy. My "more" likely scenario is a draw with the war almost as is. For France it looks like what just went, but now we can think of British possessions too. Here I find merely getting colonies returned the most likely "best" result. But I think it has a lot of fun twists.
if Britain pressures Japan in returning German possessions it could break their alliance. You get the divergence the WNT set in motion for Japan to feel slighted. Could the Germans have sold the pacific islands to the USA? That gives us a bit of a mess. If Germany must concede to Japan then we set in motion a long term animosity that could be stoked into some future showdown not unlike Germany backing China as OTL. We further alienate Australia to the UK's disadvantage. And so on.
Short of a victory where I guess you just write what you want, the most plausible scenario I get is the African colonies returned, no additions, the Pacific islands a maybe and Quingdao lost. Sad too because I have tried to imagine a German Hong Kong.