"Who is the president?"
For example,if you are asking who is the president to the people in a room "kim başkan" is correct. But if you are asking about an unspesific person, "başkan kim?" is the right one to choose
As far as my knowledge of the language goes, it is unless there was a very special way that you needed to change the stress. The best way to think about how to form questions in Turkish is to imagine how you would ask the question in shock ("The president is WHO?!).
"Who is the president?" Translation: Başkan kim?
"Başkan kimdir?" - Baska doğru Türkçe cevap.