How do I punish my opponent's opening-mistakes?

Neither of those are mistakes necessarily. They aren't the best moves, but they're at best inaccuracy (to use the lichess vernacular)

As Sarg0n said, you need to look at the position and and figure out what weakness they are showing, or why that's not a good move. (Early queen development presents a valuable vulnerable piece for instance.)

In closed positions there might be no tactictal refutation; it can be a complex strategical one or none at all. The second example can easily fit into regular Bogo Indian theory...

Btw, what do you mean by refutation: equalizing as Black, small advantage or winning outright?