A phrase used to indicate one's surprise. Well, what do you know—we have chocolate chips in the cabinet after all.

A rhetorical question meant to indicate that one's opinion or claim isn't trustworthy, believable, or welcome. Sometimes used ironically or sarcastically. A: "You really shouldn't be eating so much red meat." B: "Ah, what do you know? Red meat helps make you strong!" A: "All the healthcare experts out there say babies ought to be breastfed exclusively." B: "Bah, what do they know? My siblings and I were all bottle fed, and we turned out just fine." So, what, you think I'm wrong about climate change because of some article you read on Facebook? I mean, I only have a PhD in climatology, what do I know?"