He shares what's left (6)
I believe the answer is:
coheir
'left' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's an association between them I don't understand?
'he shares' is the wordplay.
I cannot really understand how this works, but
'he' is within the answer.
The remaining letters 'coir' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'what's' is the link.
Can you help me to learn more?
(Other definitions for coheir that I've seen before include "Not the only one to succeed" , "one of several in succession?" .)