Unfortunately, you can't really ask this question in English. You need to do a workaround. Where does Obama stand in the succession of presidents of the US? What number president is Obama? (He's number 44.) How many presidents were there before Obama? Obama is the what-number president of the United States? **Although the last one is a bit strange, it is probably the easiest way to tell someone exactly what you are asking.

simpley: who is the 44th president of the United States? or , who is Obama?

As an English learner, I'll put in my two cents. During my learning of English, I've asked myself the same question too. I looked up in some books, asked a couple of people, and what I found out was really surprising to me: The English language doesn't have a question word for the concept of "what ordinal number" like some other languages do. In Mandarin, there's 第幾 or 第几. And if I remember correctly, Japanese and Spanish have a question word like that as well. Therefore, as far as I know, the answer to your question is: No way you can ask a question like that in English, at least not in an easy or natural way.

I agree with SFull. Simply: " Is Obama the 44th President of the United States?" In future, to change a simple sentence into a question, it is necessary to change the word order to move the verb to the front of the sentence and add a question mark to the end of the sentence.

As Antman says, search this same question on Google, and you'll see that there is no interrogative for ordinal numbers in English. ( For some reason the same question always uses Obama. No one ever asks "How do you ask which number president was Filmore?" : ) And other languages do have an exact question word for that. But English speakers still find ways to ask about ordinal numbers...hmmmm.