Probably this is the first question on this particular issue here on ELL, but it's been asked many times before on ELU.
That link is to the one kept open while duplicates are closed (about once a month!).
As the answers there will show, there isn't any "natural" way to succinctly phrase such a question in English.
Informally, people sometimes ask things like
"Obama is the how-many'th president of the US?"
"This question is the what'th on the subject?".
but they're not at all standard.
The best I can think of that remains strictly "grammatical" is... "
What is the ordinality of Obama among US presidents?
" ...
but I don't recommend learners bothering with that either, since not all native speakers would even understand you.
Although it's not really "correct", most people would probably just ask something like... "What number president is Obama?"
ell.stackexchange.com/users/126/FumbleFingers Reinstate Monica
I don't particularly like the way this sentence sounds, but I think it's the clearest way to ask your question without being over-elaborate: What number president was Taft?
So I suggest you say that.
But since I don't really like the sound of it, I'll discuss a few other ways to say the same thing: I like this sentence much better, but it's pretty ambiguous: Which president was Taft? . . .
so we could probably clarify it a bit.
In informal speech, I might say the following: Which president was Taft, like the thirtieth?
Thirty-first?
Less informally: Which president was Taft?
For example, was he the thirtieth president?
Since I gave examples of answers, it's clear what I meant.
You can, of course, spell out exactly what you mean.
I avoided doing so because it's difficult to do so concisely .
We can write the following sentence, which is precise and acceptable: In the chronological sequence of Presidents of the United States, which position did
Taft occupy? . . .
but it sounds unwieldy to me.
ell.stackexchange.com/users/230/snailplane
You have your answer in the question itself!
Which position is Obama at on the list of American Presidents?
And the answer is...
He's 44th on the list of American Presidents.
ell.stackexchange.com/users/3187/Maulik V
A simple way to ask this kind of question and a way that many speakers do opt for, is with "How many".
How many American presidents (did we have|were there|came) before Obama?
-- He's the 44th president.
How many people were ahead of you in the customer service phone queue?
--I'm third in line.
How many times has he been absent?
--This is his fourth absence.
If you need more precision than that, then you're probably writing or speaking in a specialized domain where unwieldiness plays second-fiddle to precision: In which offset of the array was the string value found?
What is the item's position in the job queue?
ell.stackexchange.com/users/10264/Tᴚoɯɐuo
If I understand your question correctly, you mean position as in 9th, 10th, 11th etc.
If so you could say:
Was he the 10th president of the United States?
ell.stackexchange.com/users/None/
I would use this: At what number does Obama stand in the sequence of American Presidents?
Another option though not so good:
What is Obama's serial number among the American Presidents?
ell.stackexchange.com/users/4977/Neil D'Silva
How to ask the position(?) of a president (like 10th) of a country, correctly?
Asking the position of a person in a sequence
ell.stackexchange.com
<questions><ordinals>
ell.stackexchange.com/questions/4587
ell.stackexchange.com/users/148/Nalaka526
A simple way to ask this kind of question and a way that many speakers do opt for, is with "How many". Or "Was he the 10th president of the United States?" A more natural, but more ambiguos question would be "Which president was Taft?" Although it's not really correct, most people would probably just ask something like  "What number president is Obama?" Which, many, position and ordinality are options. You can also ask what number.
Which, many, position and ordinality are options. You can ask what number.