If someone asks me "when does school start again" and if I don´t know the answer should I say:
1 I don't know when it starts.
or
2 I don't know when it does start.
It's extremely unlikely in the specific cited context, but in general, this kind of "do-support" is used to convey emphasis (particularly, emphatic refutation of a claim made or implied by someone else). In speech, the word do (or does, don't, etc.) usually carries heavy stress, which also reflects that emphasis.
Thus I do love you could either occur as a response to your distrustful partner having said I don't believe you love me, OR it could be a spontaneous declaration of extreme affection (I really love you very much indeed!).
I can just about imagine a native speaker coming out with OP's version #2 if the intended meaning is to emphasise that maybe school won't start again. But more likely that would be expressed as...
I don't know if it will [ever] start again
answered Mar 28 '20 at 19:03
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But what if I want to say that I don´t know when it will start knowing that it will start soon? – coolguy Mar 28 '20 at 19:17
