Doctor, for example, initially studying remains (5)
I believe the answer is:
dregs
'remains' is the definition.
(thesaurus)
'doctor for example initially studying' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor').
'for example' becomes 'eg' ('e.g.' can be a synonym of 'for example').
'initially' says to take the initial letters.
The initial letter of 'studying' is 's'.
'dr'+'eg'+'s'='DREGS'
(Other definitions for dregs that I've seen before include "Bottom of the barrel" , "Parts of least value" , "Lees - riffraff" , "Grounds; refuse" , "Sediment - rabble" .)