Soldier's laugh, after knocking back some bubbly (6)
I believe the answer is:
gurkha
'soldier's' is the definition.
(term for a Nepalese soldier of the British Army)
'laugh after knocking back some bubbly' is the wordplay.
'laugh' becomes 'ha'.
'after' says to put letters next to each other.
'knocking back' says the letters should be written in reverse.
'some bubbly' becomes 'Krug' (type of champagne).
'krug' in reverse letter order is 'gurk'.
'ha' after 'gurk' is 'GURKHA'.
(Other definitions for gurkha that I've seen before include "Nepalese member of British army" , "British soldier recruited overseas" , "Nepalese fighter?" , "Soldier from Nepal in Indian or British armies" , "Nepalese soldier in the British army" .)