My hunch is that 90-99% of all Jeopardy questions can be answered with information in Wikipedia/Wiktionary, properly understood.

So I'd start with Wikipedia: ~30GB uncompressed full article text. Break it into chunks; canonicalize phrasings to be more declarative, and include synonyms/hypernym/hyponym phrasings (via something like WordNet), so that various 'cluesy' ways of saying things still bring up the same candidate answers.

Because it's free and compact and well-structured, throw in Freebase, too.

Jeopardy goes back to certain topics/answers again and again. So I'd scrape the full 200K+ clue "J!Archive", and use it as both source and testing material (though of course not testing the system on rounds in its memory).

And I'd add special interpretation rules for commonly-recurring category types: X-letter words, before-and-after, quasi-multiple-choice, words-in-quotes.

I think such a system might get half or more of the questions in a typical round correct, and in a matter of seconds, even on a single machine.