Copper gets point of prompt (3)
I believe the answer is:
cue
'prompt' is the definition.
(cue can mean a prompt or signal)
'copper gets point' is the wordplay.
'copper' becomes 'Cu' (chemical symbol).
'gets' is a charade indicator (letters next to each other).
'point' becomes 'e' (compass point).
'cu'+'e'='CUE'
'of' is the link.
(Other definitions for cue that I've seen before include "Potter" , "Rod used in billiards" , "Hint, prompt" , "Snooker player's stick" , "Sports implement" .)