Origin of snog; from uncertain or unknown; perhaps
verbsnogged, snog·ging, snogs Chiefly British Slang
Origin of snogPerhaps akin to snug1.
(third-person singular simple present snogs, present participle snogging, simple past and past participle snogged)
Possibly from the same roots as snug (meaning to lie close) which one has to do for a proper snog.