Knock back a bit of Aperol, or a bold red (6)
I believe the answer is:
barolo
'knock' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'back a bit of aperol or a bold red' is the wordplay.
'back' says the letters should be written backwards.
'a bit of' indicates the answer is hidden within the clue.
'olorab' is hidden in the letters of 'aperol or a bold red'.
'olorab' written backwards gives 'BAROLO'.
Can you help me to learn more?
(Another definition for barolo that I've seen is " Wine".)