Glad to help, Manfred. J'int is a dialectical variation on joint, used here to rhyme with pint. In fact, j'int might not even be the usual pronunciation in Hopkin's natural accent, he might have used it just for the rhyme.

So a joint is a bar, speak-easy, tavern, grocery, or other type of gathering place. An old gag, possibly used by Groucho Marx, runs:

"I learned to play cards at my mother's knee . . . and other low joints."