How to complete this question ?

[Sir Shakespeare]

Hi dear friends

1- ……. religion are you ??

If you are asked to complete this sentence with one or two questions words or an auxiliary verb , what is the best answer in your opinion?

Can I say : From which religion are you ??

Is it right that using a proposition at the beginning of a sentence is informal or even incorrect ? I read it somewhere . It was written that you cannot say :
*About what are you talking ??

I am totally confused . could you explain it ?

Thanks in advance

…..

[SoothingDave]

Not a teacher.

I would just say "Which religion are you?" (Or informally, "What religion are you?" "Which" is the better word, but "what" happens.)

I am Catholic. I am not "from Catholicism."

[2006]

Not a teacher.

I would just say "Which religion are you?" (Or informally, "What religion are you?" "Which" is the better word, but "what" happens.)

I don't agree that "Which" and "What" primarily relate to formality. Nor do I agree that "Which" is necessarily better.

To me, it is the usual difference between "What" and "Which". "What" is an open question, while "Which" is usually used when one is being asked to choose from specified choices.
Overall, "What" is more commonly used. And in Sir's first sentence, I would definitely use "What".

[Sir Shakespeare]

Ok , Many thanks for your help !
I appreciate your answers

***

In order not to post a new thread , could any one just clarify this confusing question ?

Is it right that using a proposition at the beginning of a sentence is informal or even incorrect ?
Can't I say :
*About what are you talking ??

[bhaisahab]

Ok , Many thanks for your help !
I appreciate your answers

***

In order not to post a new thread , could any one just clarify this confusing question ?

Is it right that using a proposition at the beginning of a sentence is informal or even incorrect ?
Can't I say :
*About what are you talking ??

It's technically correct, but nobody would say it.