"Who him?" as a stand-in for "Who is he?"
Solution 1:
The phrase "who him" is also used in Jamaican dialect. It may mean "who is he?" , as well as "who does he think he is?." This depends on the situation in which the phrase is used and also the tone used to deliver the phrase. I tend to use it to mean "who does he think he is."
Solution 2:
"Who he" or "Who him" are idiomatic usages. They're not that common, but they are at least understood, if not very widely.