First of all, I know that if we ask "who is he.", normally the indirect question which corresponds with it would be "who he is." (for example: do you know who he is?)
Still, recently, one question has been worrying me. Here's what I'm thinking about: The way in which we form indirect questions seems to depend on how we identify the correct subject of the sentence, and this is exactly the reason why we sometimes find that the word order in both a indirect question and a direct question are actually the same, because the interrogative pronouns of the direct question happens to be the subject of the original statement. For example, if the direct question is "how many of you are hungry for success", the indirect question which corresponds with it would be "how many of you are hungry for success."
Here comes the problem: do we usually presume that in a direct question like "who is he", the subject of the original statement is "he" not "who"? (which should explain why we always say do you know who he is but not who is he). It seems to me that without this assumption there's no way we can identify the real subject in the kind of questions like "who is he".
A question like "who is he" usually comes from a statement in the form of "A is B.". From this statement, It is possible to form both "Who is A." and "Who is B." In the former question the subject is "A", and in the latter question the subject is "who". Based on the rule from which we form indirect questions, there are actually two possible indirect questions here. One would be "do you know who A is?", and another would be "do you know who is B?".
I know this is quite puzzling, and perhaps sounds very unnatural to the ears of natives. But I really want to be sure whether sentences in the form of "do you know who is he." are truly grammatically wrong. I actually came across some cases in which there seemed to be nothing wrong with the usage of "do you know who is he".
(This one, for example: http://thegrammarexchange.infopop.cc/eve/forums/a/tpc/f/340600179/m/8046085494