system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel/DC] What does Wikipedia look like? Does it have information on cosmic beings? What sort of obscure facts about superheroes and aliens could I find on there?
gpt
Major public heroes, it likely has a lot of surface level information on- you could probably find out superman's public appearances, powers,weaknesses and enemies. Likewise major supervillians who are in the limelight- you could get the joker's past crimes (he may well update it himself). Big teams will have headquarters and rosters and leaders and such like. Very large concepts, like the mutant gene, will have scientific pages.

More secret/esoteric stuff is far sparser, simply because fewer people know enough to edit. Subtle heroes like daredevil and batman are more in the vein of urban legends then superheoes. Most interdimensional and extraterrestrial information is vague at best: you might get that Krypon is superman's dead home planet, but that's about it. Likewise concepts like the Speedforce or the Green or the Infinity Gauntlet- likely just a short article with "we don't know much" at best.

Generally, it would be much like any other topic- a good starter but no substitute for in depth study. You could learn who superman is and where he's been seen, but its not going to get you an in-depth analysis of kryptonian biology.