"Per chi è il pollo?"
Traduzione:For whom is the chicken?
"Who" is used as the subject in a sentence, "whom" is used as the object in a sentence and also after a preposition. But don't worry too much about it, 99% of English speakers don't use "whom" at all, we just say "who" instead. "Whom" is more for academic writing. For the sentence above I would say "who is the chicken for".
As far as I know, in spoken language, the sentence sounds like this: who is the chicken for?....."for whom is the chicken" is correct, maybe too much :) a very formal language