Could the US take Papua and/or the Bismarck Archipelago from Germany?
The US, if interested/willing in acquiring territory in the war at all, would be more interested in gaining Palau, the Carolines, Marshalls, and Marianas. Essentially, all of German (formerly Spanish) Micronesia. Samoa would be nice, but it'd be more important to concede German Samoa to the British/Australians/New Zealand in return for their support of American annexation of Micronesia.
Why in the world would the US want Micronesia? War Plan Orange, the series of paper planned strategies for war with Japan. German acquisition of Micronesia posed a problem to American naval strategists, as in the event of war between the US and Japan, the Philippines and Guam would be isolated and subject to local Japanese military superiority. Bringing the full force of the US navy would be very difficult, not just because of the distance involved, but also because there would be no certain (or secure) fleet anchorages for coaling, repair and resupply.
IOTL, Japan's occupation of the Micronesian islands actually solved that problem by giving the USN an intermediate target. In the case of war, fleet anchorage could be gained by step-wise conquest and pacification leading toward the relief or liberation of the Philippines and Guam. The US of course had no opportunity to gain German territory IOTL given its late entry, and Wilsonian pledges of self-determination and non-annexation.
ITTL, Japan probably grabs German holdings in China, but is beaten to the punch in Micronesia and elsewhere. The strategic value of those Pacific island chains to the US (and Japan) strongly suggests that they'd be a major gain for one or the other, and in a case where the US has been shedding a great deal of blood in the trenches, the American President will need to have something to point to as a gain from the war, however trivial it may seem.