pick your brain 

To probe for answers

If you have a minute to spare, I'd like to pick your brain about lachrymology.

pick your brain by DGirard July 17, 2005

pick your brains 

understand more, in detail and in general, to learn someone's behaviour and the nature of how someone thinks, what motivation of the persons actions, what triggers the feeling etc.

I'd like to pick your brains out, let's have an in-depth discussion on this...

pick your brains by Rico Fikri December 15, 2008