Exploiting wrong deviations from theory in chess openings What are some good sources about exploiting wrong deviations from standard chess theory during the opening? That is, given the fact that the opponent steps out of the canonical openings, and is not innovating a variant with style and making it stronger.
I would recommend the Chessok Opening Tree.

You can browse the lines you are interested in and see which moves have already been played (which at the beginning of an opening is almost every halfway sensible move). And most importantly you'll get an engine evaluation for each move, which immediately tells you which of these halfway sensible moves is a blunder. 

If you are further down the rabbit hole and the line has never been played before, of course you have to rely on your own chess understanding to come up with the most likely human moves and can then use an engine to find out how to punish them. Online, this would be possible on Chess24, though as non premium member you might have to wait a while for the engine evaluation to come up.