What are the questions science cannot answer?

what is dark matter?

The term "Dark Matter" already implies a posed answer, it's no that it can't be answered it's whether the answer is scientifically provable as opposed to being a pseudoscience.
No one knows.

No one can know, actually, at this early going.

Not even the OP question is definitely unanswerable via an appropriate science of some future kind.
why i'm sitting in the sun squinting at my laptop, when i could be inside on the couch, not squinting at the screen.