A wh-question

[Munawar Iqbal]

I have been searching for a question word in English. It exists in many languages but I do not know how they say it in english.

what may be the question of the following answer.

It is my SIXTEENTH birthday.

Is it right to ask : What is the number of your next birthday.

I would be obliged if anybody clarifies.

[monty mike]

You could ask, 'How old will you be on your next birthday?' But then it makes more sense to ask 'How old are you?'

For someone to answer 'It is my SIXTEENTH birthday', you would have to ask them 'How old are you today?' on their birthday.

[Raymott]

I have been searching for a question word in English. It exists in many languages but I do not know how they say it in english.

what may be the question of the following answer.

It is my SIXTEENTH birthday.

Is it right to ask : What is the number of your next birthday.

I would be obliged if anybody clarifies.

This has been asked recently in the form of "What number President of the US was Clinton?" There is no simple English term. Maybe we should have "what'th" or "whichth". "What'th's your next birthday? Whichth President was Clinton?"
But we don't!