I think '누구의 머리카락은 짧아요?' is a sentence asking does anybody has short hair....(and it is little bit awkward) the right one for english one is '누구의 머리카락이 짧아요?' Any way 은 is awkward...im native speaker

Can you say "who has short hair" or would that need 짧은 머리카락 in the sentence?

I put who has short hair as it is more colloquial in British English.