I want to find out more about the lore of a specific card game (specifically MTG). Would this site be where I would ask questions regarding it, as they are questions regarding to a board game, or would I be better off asking them on the Fantasy Stack Exchange?
Lore questions on here are fine by current policy. They are also on topic for Sci-Fi & Fantasy SE as long as the game has science fiction or fantasy elements; SFF has a MTG tag. You may ask on either one, since Stack Exchange network practice acknowledges sites can have overlapping topicality and allows that you can ask on whichever you want that services the topic. (Please don't ask it on both though, since the network community frowns on cross-posting.)
We've touched on this twice before and the community's come out firmly in favour both times:
We're interested in board & card games but we're not limiting ourselves exclusively to their gameplay and have found it useful to explore areas around our games too.
I'm not sure how much ground we've covered in this vicinity though. Many of our games of course don't have lore at all, or not any lore that extends beyond the game materials we play with. In Magic: the Gathering specifically, which you've asked about, I could find three lore questions, and only the first one is directly asking about the nature of the lore:
- Does the MtG lore have an official explanation for banned cards?
- Where can I find the story of Magic the Gathering?
- Are there Magic: The Gathering lore books for the recent blocks?
Stack Exchange works best when dealing with actual situations people face, and that's true for establishing meta policy as well. If lore questions turn out to be a problem subject, something we can't handle well or elect that we shouldn't handle, more lore questions on the site will help us discover what we need to do. If they're fine for the site, then all's well.
Please do ask away about game lore here if you'd like.