Green’s Dictionary of Slang

(N.Z./UK) to hit, to thump.

1951, 1953		in DNZE questionnaires.
1964		N.B. Harvey Any Old Dollars, Mister? 59: It went s-sonk! and he spat out the bottle top and started sozzling away.
2003		McGill Reed Dict. of N.Z. Sl.
2023		R. Milward Man-Eating Typewriter 43: [S]chonking me repeatedly with the powder-puff.