If it were asked "Who are you the attorney for?", it sort of seems like "Who" is the subject. Think of the equivalent question "Who is your client?" That clearly has "who" as the subject.
So it can't be simply the order of the words, can it? Does it have something to do with the fact that my proposed rewrite ("Who are you the attorney for?") on ends in a preposition? I understand from you Arts Majors that this is a bad thing. Are they connected? Are we not supposed to end sentences in a preposition because they improperly make it seem as the object of the sentence is actually the subject?
If anyone can answer these probing questions, I figure it's you.