For specific ear plugs, Loop earplugs and the Flares Calmer earplugs are some of the best I've found as an AuDHD person. Flares in particular. They take the "edges" off sounds and are so subtle I regularly forget they're changing anything until I take them out, and then the world hits me in the ears and I quickly put them back in, lol. Loops are great for blocking heavy noise, and good for those of us with small or oddly-shaped ear canals. Their unique base shape allows me to turn them in a way that "braces" them against my ear and helps keep them in place. Also, they are the least obtrusive I've found as a side sleeper.
Neither will stay put very well if you're chewing or talking a lot, but that's been true of every earplug I've ever tried. Jostling loosens things, it's simply a fact. I wanted to at least mention it, in case "I need to block sound while chewing" is your need, but for anyone else, please don't let that deter you. They are a little bit pricy for a few grams of silicone that go in your ear, but I fucking love these things. You may be able to find them more cheaply as knock-offs elsewhere, too.
As far as studying goes...
Take Notes. Take as many notes as you can in class. Not after class!! IN CLASS. Take notes like your life depends on it, and doodle in the margins to stay focused until you realize there's a new slide you need to write down. Handwriting helps stuff stick.
Then, the night before the exam at the latest, get a new notebook. Copy your notes from class into the new notebook. All of them that will be on the test. By hand.
(Remember to shake out your hands periodically! Loose fingers, loose wrists, and wrist-twist while bouncing your elbows to shake your hands out! This is a pianist's trick to help stay limber, and it works just as well for handwriting. Do Not give yourself tendonitis. Learn from my mistake. If it hurts, stop. Your grade is not worth your health. Do NOT give yourself tendonitis in your hands; it will turn into carpal tunnel and you Do Not Want That. DO NOT.)
Copy all your notes by hand. If you are able to start a few nights before, great! This will show you what you're uncertain about, based on how much you're able to remember while copying. (You may remember bits and pieces from the lecture as you copy, because your brain made an association web while you were writing by hand the first time.) If not, THAT'S OKAY!!!! Every little bit counts! Copy as much as you can the night before the test. If you are rocky on some of it, try to copy those parts twice, but if you can't, OH WELL!
Go to sleep right after you finish writing. Shake out your hands, take a shower if you must, and GO TO SLEEP while your writing memories are still fresh. This sounds kinda like woo-woo nonsense, I know, but I never learned to study in high school and this is the best I've got. (It landed me two degrees in accounting, so...meh?)
If you cannot write by hand, type. If you cannot type, banish your roommate and speak out loud. Scan the chapters with your eyes and talk to an invisible audience as if you were trying to teach them. For me, writing was best, but speaking definitely also helped.
Important: If you have the "in one eye, out the other" inability to parse boring text, reading out loud like a newscaster (or Captain Kirk) is going to be your best friend. Example:
Snell's law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air. In optics, the law is used in ray tracing to compute the angles of incidence or refraction, and in experimental optics to find the refractive index of a material.
Boring. I cannot read this. But, if I pretend I am an overly-chipper news anchor at 6:45AM on Good Morning America:
SNELL'S LAW is a formula used to describe the relationship BETWEEN the angles of incidence and refraction, WHEN referring to LIGHT or other waves PASSING THROUGH A BOUNDARY between two different isotropic media, such as water, glass, or air. In OPTICS, the law is used in ray tracing to COMPUTE the angles of incidence or refraction, and in EXPERIMENTAL optics to FIND the refractive index of a material.
(that's not accounting, obviously, that's physics, but it's an example, don't @ me.)
It looks deranged, formatted that way, but hopefully you can see what I mean by using a newscaster voice. Speaking aloud and forcing strong emphasis drags your brain into line and helps break down concepts and clauses in complex sentences WAY BETTER than just staring at them.
...I think that's all I've got for you. Good luck out there, buddy. Please let me know if I should clarify anything, I'm really tired. Hopefully this is at least coherent.