Good question - this one's a little case-by-case.

If the focus of what you're discussing is specifically Star Trek, the general c/StarTrek community would be fine. If you're looking to get serious and in-depth with it, c/DaystromInstitute would also work.

If the primary focus is on the real world and the Trek connection is more tangential (examples: "cell phones were inspired by communicators" or "this new medical device is kind of like a tricorder"), it's probably more appropriate for Quark's. But there are some edge cases in there, and we're unlikely to be fussy if something ends up in c/StarTrek instead.