I am always confused about the second part. Because it seems to me that the second part is kind of a question so i should use do/ did according to tense but at the Same time it also feels weird to add do/did because it makes the whole sentence sound weird. Another example of such sentence is - "I don't know why he asked me" or "I don't why did he ask me". So please tell me which one of them is correct and if possible with examples. And I also want to Thank u you guys. You do a very good job by answering these question. This help goes a long way towards learning English.
Both are grammatically correct but I am struggling to think of circumstances in which the second would ever be used. The best I can do is this rather artificial conversation: - He asked you? That was a strange thing to do! - I don't why he did ask me. The use of 'did' responds to the 'do' from the first speaker. It puts a slight emphasis on the doing rather than on the asking or on the 'me'. Even in my artificial example, it would be more natural for the reply to be simply "I don't know why he did."