That would be unnatural. In general, we use "Who" for people and "What" for things. If you asked "What does that boy do?", you'd get "He's a student". If you asked "Who's that boy?" you might get his name, or his relationship to the person you asked, or some other information (as in post #1).
Who's that boy?
That's Samuel.
Who's that boy?
That's my cousin Samuel.
Who's that boy?
He's a student in my year but I don't know his name.