I'm back, again. I'm buying a BMX bike, its a 2021 Kink Gap XL. I wanna put pegs on it, because it doesn't have pegs, and a lot of the tricks I wanna learn require pegs. So, if I buy this bike, will I be able to put pegs on it? Will pegs work on any BMX bike? I don't really care what brand, just as long as something will work. Are there different sizes too?
To answer your specific BMX Bike
The King Gap XL 2021 will support pegs. It's safe to say that any freestyle BMX bike will support pegs. If you were buying a BMX race bike, there's a chance it doesn't support pegs; BMX race is more focused on being lightweight than freestyle BMX.
Can I put pegs on any bike
No, you need to have a certain type of axle to put on pegs. It won't work on a dirt jumper / mountain bike / road bike for example. The axle needs to stick out from the fork / dropouts to have room to house the peg. There's a nut that screws onto the outside of the peg, so if the axle doesn't have the thread, it won't work.
Now compare that to a MTB axle - this is a 15 x 110 boost axle, which is super common on MTB front wheels.
Words of advice
Buy plastic pegs so you don't ruin skatepark ledges