Doctor has endless discussion after coffee (5)
I believe the answer is:
mocha
'coffee' is the definition.
(type of coffee drink)
'doctor has endless discussion' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'has' means one lot of letters go next to another.
'endless' means to remove the last letter.
'discussion' becomes 'chat' (chat can mean a conversation).
'chat' with its final letter taken off is 'cha'.
'mo'+'cha'='MOCHA'
'after' is the link.
(Other definitions for mocha that I've seen before include "Kid" , "It may end up as grounds" , "Fine quality coffee" , "Yemeni port; type of coffee bean" , "Deep brown; a fine coffee" .)