GI’s jaw is broken? It’s a puzzle! (6)
I believe the answer is:
jigsaw
'a puzzle' is the definition.
(jigsaw puzzle is a kind of puzzle)
'gi's jaw is broken?' is the wordplay.
'is broken?' indicates anagramming the letters.
'gis'+'jaw'='gisjaw'
'gisjaw' with letters rearranged gives 'JIGSAW'.
'it's' acts as a link.
(Other definitions for jigsaw that I've seen before include "Puzzle in which pieces must be reassembled" , "Sharp tool (for cutting puzzle into pieces?)" , "Type of puzzle" , "Picture in pieces" , "Problem with fitting in" .)