what do you know

(well) what do you know

A phrase used to indicate one's surprise upon discovering something. Hey, what do you know—we have chocolate chips in the cabinet after all. Well, what do you know! It says here that my ancestors first came to this country in 1857!
See also: know, what

What does (one) know?

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?"
See also: does, what
Farlex Dictionary of Idioms.

what do you know

What a surprise, as in What do you know, our suitcases are the first off the plane. [Early 1900s]
See also: know, what
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • (well) what do you know
  • what do you know!
  • What do you know?
  • How long is a piece of string?
  • from my cold, dead hands
  • eggs is eggs
  • going, going, gone
  • going, going, gone!
  • how about
  • how/what about...?