Envoy's graduation certificate required on top of those (8)
I believe the answer is:
diplomat
'envoy's' is the definition.
(I've seen this before)
'graduation certificate required on top of those' is the wordplay.
I cannot really see how this works, but
'certificate' could be 'diploma' (diploma is a kind of certificate) and 'diploma' is found in the answer.
A single letter 't' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for diplomat that I've seen before include "An ambassador or tactful person" , "Foreign representative" , "tactful one" , "Tactful government official" , "Tactful type" .)