how's it right?

[Olesya_Altynbaeva]

I'm a little bit confused about one grammar structure. for example: what happened to that gold watch you used to have? This is a question. But it hasn't got an auxilary verb, like "do" or "have" Why don't we ask: what did it happen to ...?

[Hedwig]

I'm a little bit confused about one grammar structure. for example: what happened to that gold watch you used to have? This is a question. But it hasn't got an auxilary verb, like "do" or "have" Why don't we ask: what did it happen to ...?

I think it's because what is the subject of the question.
In, for example, what did you do to that gold watch you used to have? you'd use the auxiliary, but the subject here is you.

Hedwig
Not a teacher