Green’s Dictionary of Slang

1. (Irish) to sniff out news and gossip.

1939

P. Gallagher My Story n.p.: Just say that you heard there was bad stuff in Brennan’s, you know how that Anna one would be snooking for news [BS].

2. (UK prison) to look through; thus snook the Judas v., to look through the observation window or ‘Judas hole’ in a cell.

1954

J. Phelan Tramp at Anchor 127: He only ‘snooked the judas’ once during the night.