Surrender? I don't know! (4,2)
I believe the answer is:
give up
I believe this clue is a double definition.
'surrender?' is the first definition.
(I know that give up can be written as give up)
'i don't know' is the second definition.
('give up' can mean you don't know the answer)
(Other definitions for give up that I've seen before include "Cease trying" , "Cede, forego" , "Resign" , "Throw in the towel" , "Surrender or abandon hope" .)