Assume you’ll agree to stand (3)
I believe the answer is:
don
'assume you'll' is the definition.
'don' can be an answer for 'assume' (thesaurus). I am not sure about the 'you'll' bit.
'agree to stand' is the wordplay.
'agree' becomes 'nod' (I've seen this before).
'to stand' is a reversal indicator (I've seen 'standing' mean this).
'nod' back-to-front is 'DON'.
Can you help me to learn more?
(Other definitions for don that I've seen before include "Put on; man's name" , "Put on clothes like noss" , "A mafia chief or Spanish lord" , "Spanish nobleman" , "Put on; lecturer" .)