He takes interest in his work (11)
I believe the answer is:
moneylender
'interest in his work' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he' is the wordplay.
I cannot really see how this works, but
'he' could be 'der' and 'der' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'takes' is the link.
Can you help me to learn more?
(Other definitions for moneylender that I've seen before include "Usurer" , "One advancing at interest" , "Loan provider" .)