"I didn't ask about this", "I didn't ask this question", "I didn't ask this" - do these three versions have the same meaning amd are correct in a situation when I want to say that it wasn't me who asked that question, but someone else?
You could use any of those sentences to express the meaning you have stated. However, your later comment in the text is actually the most clear:
It wasn't I who asked that question.
This makes it explicitly clear that the question was asked, but by someone other than you.
The other three sentences might be used to clarify that the speaker did ask question, but a different question. However, the context of the situation would probably make your original intention clear. Emphasis would also make the meaning clear, especially in spoken dialog.
I didn't ask this question.
The emphasis on "I" implies that someone else asked the question.