Doctor's holding for example, remains (5)
I believe the answer is:
dregs
'remains' is the definition.
(thesaurus)
'doctor's holding for example' is the wordplay.
'doctor's' becomes 'drs' ('Dr' can be a synonym of 'doctor').
'holding' is an insertion indicator.
'for example' becomes 'eg' ('e.g.' can be a synonym of 'for example').
'drs' enclosing 'eg' is 'DREGS'.
(Other definitions for dregs that I've seen before include "Bottom of the barrel" , "Leftover drink, sediment" , "Fluid remnants" , "Dross" , "Liquid remnants with sediment" .)