Kiss in Kent (4)
I believe the answer is:
'kiss in kent' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for snog that I've seen before include "Amorously kiss" , "Cuddle, kiss (slang)" , "Kiss and cuddle (sl.)" , "Pet" , "Indulge in amorous activity" .)