Found out officer's about to make money (6)
I believe the answer is:
learnt
'found out' is the definition.
(I've seen this in another clue)
'officer's about to make money' is the wordplay.
'officer' becomes 'lt' (abbreviation for lieutenant).
'about' indicates putting letters inside.
'to make money' becomes 'earn' (to earn is to make money).
'lt' going around 'earn' is 'LEARNT'.
(Other definitions for learnt that I've seen before include "Realised" , "Acquired knowledge or skill" , "Aquired knowledge or skill" , "Heard" , "Memorised" .)