Enjoy including a negative relation in identification (9)
I believe the answer is:
diagnosis
'identification' is the definition.
(I know that diagnosis is a type of identification)
'enjoy including a negative relation' is the wordplay.
'enjoy' becomes 'dig' (to dig can mean to appreciate or 'get').
'including' is an insertion indicator.
'negative' becomes 'no' (no is a kind of negative).
'relation' becomes 'sis' (sis is a kind of relation).
'dig' placed around 'a' is 'diag'.
'diag'+'no'+'sis'='DIAGNOSIS'
'in' acts as a link.
(Other definitions for diagnosis that I've seen before include "doctor's opinion" , "Identification of a problem from its symptoms" , "Interpretation of" , "Identification of disease" , "Doctor's verdict" .)