Spooner's diver could have second job (9)
I believe the answer is:
moonlight
'have second job' is the definition.
(moonlighting can mean doing a second job secretly)
I cannot understand how the remainder of the clue works.
(Other definitions for moonlight that I've seen before include "Burn the midnight oil" , "Hold a second job" , "Perform work at night" , "Lunar rays seen in thin gloom" , "Ray" .)