Finds out that money makes money (6)
I believe the answer is:
learns
'finds out' is the definition.
('learn' can be a synonym of 'find out')
'money makes money' is the wordplay.
'money' becomes 'l' (L can mean 'pounds').
'makes money' becomes 'earns' (I've seen this in another clue).
'l'+'earns'='LEARNS'
'that' acts as a link.
(Other definitions for learns that I've seen before include "Discovers" , "Gains understanding from study or experience" , "Finds out" , "Acquires knowledge or skills" , "Imbibes knowledge" .)