Who in class knows what’s said by gunman? (5,2)
I believe the answer is:
hands up
I believe this clue is a double definition.
'who in class knows' is the first definition.
(asking a class to put their hands up)
'what's said by gunman?' is the second definition.
(a gunman might tell you to put your hands up)
(Other definitions for hands up that I've seen before include "Highwayman's instruction" , "armed robber's demand" , "Who knows" , "Don't resist, I've a gun!" , "call for surrender" .)