What do you know for sure?

What do you know for sure?

Inf. How are you?; What do you know? (Familiar. An elaboration of What do you know? Does not require a direct answer.) Tom: Hey, man! What do you know for sure? Bill: Howdy, Tom. What's new? John: How are you doing, old buddy? Bill: Great, John! John: What do you know for sure? Bill: Nothing much.
See also: know, what