Dope is surprisingly self-assured (6)
I believe the answer is:
poised
'self-assured' is the definition.
(I've seen this in another clue)
'dope is surprisingly' is the wordplay.
'surprisingly' is an anagram indicator (a surprising ordering of the letters).
'dope'+'is'='dopeis'
'dopeis' is an anagram of 'POISED'.
(Other definitions for poised that I've seen before include "Self-possessed or balanced" , "Showing self-assurance" , "Balanced or self-assured" , "Elegant, self-assured" , "Balanced and composed" .)