help to make a question

[m@ys@m]

hi every body i am iranian i've been trying to make a question but i can't i want native american and english people lend me a hand
the question is about knowing the rank of a president
for example
i say j.f. kenndy is the 50th president of usa

and when i don't know the rank of this president how should i make a question so that the answer is he is 50th president of usa
i wanna know how native people make a question of this sentence

i hope you understand me

for example
when i say i am 18 years old

and when you don't know my age you
ask me

how old are you?

now what about this

answer : j.f.kenndy is 50th president of usa.

question : ?????????????(tell me how to make this question)


thanks in advance

[Daydream]

Who was the 50th president of the United States?

or

What presidential number was J.F.K.?

**on a side note.. I don't think J.F.K. was the 50th president hehe so just in case that wasn't a quick sample question you may want to check that out to be sure before you ask..

[Drummer for Vertiis]

Question: What number president was John Fitzgerald Kennedy?

Answer: He was thirty-fith (35th) Presedent of the United States Of America