There are some relevant suggestions in Leil Lowndes's book How to Talk to Anyone:

[W]hen you crave a bigger hit of insider lingo, start reading trade journals. Those are the closed-circulation magazines that go to members of various industries. Ask your friends in different jobs to lend you one so you’ll have even more fuel for the conversational fire.

All industries have one or two. You’ll see big glossy rags with names like Automotive News, Restaurant Business, Pool and SpaNews, Trucking Industry, and even Hogs Today for people in the pig business. (Excuse me, they call themselves “swine practitioners.” Hey, you never know when, to make your next big sale, it will help to speak pig.) Any one issue will give you a sample of their lingo and inform you of the hottest issues in that field.

When it comes to people’s hobbies and interests, browse through magazines on running, working out, bicycling, skiing, swimming, and surfing. Large magazine stores carry biker rags, boxer rags, bowler rags, even bull-riding rags. You’ll find thousands of special-interest magazines published every month.

She also suggests trying out new activities yourself, just for the sake of learning more about them:

Once a month, scramble your life. Do something you’d never dream of doing. Participate in a sport, go to an exhibition, hear a lecture on something totally out of your experience. You get 80 percent of the right lingo and insider questions from just one exposure.

(cf. Eliezer's "A New Day")