Doctor agonised about second opinions (9)
I believe the answer is:
diagnoses
'opinions' is the definition.
(a diagnosis is a medical opinion)
'doctor agonised about second' is the wordplay.
'doctor' is an anagram indicator.
'about' is an insertion indicator.
'second' becomes 's' (common abbreviation).
'agonised' with letters rearranged gives 'diagnoes'.
'diagnoes' going around 's' is 'DIAGNOSES'.
(Other definitions for diagnoses that I've seen before include "Doctors" , "medical interpretations" .)