The latest fashion for knocking back what's in Champagne domaine (4)
I believe the answer is:
Here is my best explanation:
'the latest fashion' is the definition.
'mode' can be an answer for 'fashion' ('mode' can be a synonym of 'fashion'). I am not sure about the 'the latest' bit.
'knocking back what's in champagne domaine' is the wordplay.
'knocking back' says the letters should be written in reverse.
'what's in' says the answer is hidden in the clue.
'edom' is hidden in the letters of 'champagne domaine'.
'edom' in reverse letter order is 'MODE'.
'for' acts as a link.
(Other definitions for mode that I've seen before include "Way, method", "Fashion in dome", "'Fashion, style (4)'", "Style; statistical value", "Fashion - look", "Way of doing something", "Way of doing - fashion", "Form or style", "Style of dome" and "Way of operation".)