Great kipper knocking out a cold gourmet (7)
I believe the answer is:
epicure
'gourmet' is the definition.
('epicure' can be a synonym of 'gourmet')
'great kipper knocking' is the wordplay.
'great' becomes 'epic'.
'kipper knocking' becomes 'ure' (I can't explain this - if you can you should believe this answer much more).
'epic'+'ure'='EPICURE'
'out a cold' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for epicure that I've seen before include "Lover of fine food and drink" , "Connoisseur" , "One enjoying fine food and drink" , "Lover of fine foods" , "Person with refined tastes in food and drink" .)