Senior policeman, one doubting male medical specialist (13)
I believe the answer is:
diagnostician
'medical specialist' is the definition.
(I know that diagnostician is a type of medical specialist)
'senior policeman one doubting male' is the wordplay.
'senior policeman' becomes 'di' (detective inspector. I am not sure about the 'senior' bit.).
'one doubting' becomes 'agnostic' (someone unsure on the topic of religion).
'male' becomes 'ian' (I've seen this before).
'di'+'agnostic'+'ian'='DIAGNOSTICIAN'
Can you help me to learn more?
(Other definitions for diagnostician that I've seen before include "disease expert" , "Identifier of illnesses" , "Vet, perhaps" , "he may identify your problem" , "doctor" .)