Consider what makes something funny to you. (There are no right and wrong answers here! Whatever makes humor work for you is what you want to get a better understanding of--because it's really, really hard to write a deliberately and authentically funny character when you the author wouldn't actually consider them funny yourself)
Broad strokes/genre of humor is part of it. Maybe you like dry wit, or biting sarcasm. Maybe you like lighthearted silliness and fun-poking. Maybe you like puns, wordplay and dad jokes. Maybe you like your jokes more formulaic. Maybe deliberate joking around for the sake of joking isn't your thing, but you love a good story with humorous observations and a dash of light-hearted self-deprecation. Maybe you find humor more in situations and visuals than in any verbal form of humor.
Then there's content of the jokes. Do you like them soft and sweet and kind? Do you like a bit of a bite to them? Do you enjoy it when they play with that line between taboo and not taboo, risque and not risque? Where's the line for you between "haha" and "dude not funny", and does it depend on context and/or who is doing the joking? (E.g. for me, I don't appreciate jokes that are built upon autistic stereotyping and the likes--unless they're made by a fellow autistic, because then they're not poking fun at autism, they're poking fun at the rampant stereotyping)
But then look deeper.
Even if a joke or pun or humorous situation should be right up your alley, and subject-wise lands square in what's your sweet spot, that doesn't automatically make it a good joke, right? So consider what else plays into your perception of humor.
Non-verbal communication, like facial expression, body language, and tone of voice.
Say you like puns. Does a pun land better for you when someone tells it with a straight face, and you get that "wait a second..." effect with a couple seconds delay? Or is it when someone's trying to say it with a straight face, but they can't stop their eyes from twinkling and corners of their lips from twitching? When someone's outright giggling at their own silliness? When someone makes a pun on accident?
How about tone of voice? Deadpan delivery to go with that straight face, laughter in their voice to go with their twinkling eyes and twitching lips? Or a tone of voice that contrasts with their expression/body language? Or maybe you actually prefer seeing them written, and tone of voice and body language work best for you when they're both absent.
Setting, timing, other people.
What about setting and timing--do puns land better for you if they're made when everyone's in a relaxed, possibly even silly mood, or when they're used to cut through a tense atmosphere? Are there puns you'd laugh at among friends or family, but would cringe at in the workplace, or vice versa? Are there puns you would laugh at when stressed, but not when relaxed? Are there situations where a bad pun might startle you into laughter even though it's really not that funny? Times where an otherwise good pun would only serve to get on your nerves? How does the presence or absence of other people hearing the same thing play into your perception of a joke?
The person telling the joke.
Ever met someone you didn't want to consider funny, but still found funny anyway? Had any good jokes or puns ruined for you because they were told by an absolute asshole? People you find funny from a distance, but know would get on your nerves in two seconds flat if you actually had to interact with them? But also stuff like...subverting expectations. A teenager dropping an f-bomb isn't particularly funny or serious in and of itself. But a prim old lady doing the same? That's either really funny or really serious, with not much in between.
Not all of these things are easy to convey in writing, and even when they're conveyed, they don't necessarily have the same effect as they would have in real life (reading a description of a facial expression isn't the same as seeing it). But knowing to what degree they play into your perception of humor can help a good bit in making your humor feel anchored rather than forced on top of a story or character, anyway (and in filtering out bits of humor that just really, really don't work in text).