Doctor is at first doubtful about identifying diseases (10)
I believe the answer is:
diagnostic
'identifying diseases' is the definition.
'diagnostic' can be an answer for 'identifying' (thesaurus). I am not certain of the 'diseases' bit.
'doctor is at first doubtful' is the wordplay.
'at first' says to take the initial letters.
'doubtful' becomes 'agnostic' (unsure about religious beliefs).
The first letters of 'doctor is' is 'di'.
'di'+'agnostic'='DIAGNOSTIC'
'about' is the link.
Can you help me to learn more?
(Other definitions for diagnostic that I've seen before include "Distinctive symptom or characteristic (of a disease)" , "Indicating the nature of an illness" , "Computer program" , "Analytical" .)