Guess attitude after drink (7)
I believe the answer is:
suppose
'guess' is the definition.
('suppose' can be a synonym of 'guess')
'attitude after drink' is the wordplay.
'attitude' becomes 'pose' (I've seen this before).
'after' is a charade indicator (letters next to each other).
'drink' becomes 'sup' (I've seen this before).
'pose' after 'sup' is 'SUPPOSE'.
(Other definitions for suppose that I've seen before include "Assume without proof" , "Fancy" , "'Believe, perhaps on uncertain grounds (7)'" , "Expect" , "Presume" .)