The Fundamental guide of how to use that dandy little Knife.
Step #1 - Learning Your Knife
The Knife has infinite durability, unlike RE:Remake 2 where they break faster than my Grandmother's hips. This is highly useful because you don't have to be conservative about it, so you can shank boys willy nilly. Seems like no downsides, right?
It's not a gun. That's the downside.
It also does about as much damage as a wet sandpaper slap (or the RE2's shotgun, take your pick). However, it's highly useful for taking down downed zombies while conserving ammo. Just make sure they don't eat your ankles. You kind of need them.
Step #2 - How to Use Knife
Now, that's all fine and dandy, but how do you use the Knife? It's actually not a sub-weapon anymore; it's upgraded to its own dandly little slot. I personally binded it 4 but that's how it is for default so just kinda bind it to whatever you want. You usually want to use your knife when there is only one zombie, as a bunch of 'em will swarm you faster than a fat dude at Golden Corral. Use it when you don't have enough ammo or use it as a major backup. However, there is a trick with the knife that I don't actually see a guide on yet.
It's called, and superior naming, I know, The Knifedodge.
If you do a perfect dodge with a knife, and you hold right and left click (i dunno how it is for whatever gamepad you use but I'm assuming it's the aim and fire at the same time) you'll do a lunge at them with Knife. Super useful for doing Knife-only or just stickin' it to 'em. I recommend learning when a zombie will lunge so you can use this ability to its full extent.
Now, if you're a major dumbass like me, you can try fighting Nemesis. I won. It's possible. And I suck real hard at this game.
Step #3 - How to Fight Nemesis with the Knife
I'mm preface this by saying this is NOT RECOMMENDED at all.
With that out of the way, this is how you beat Mr. NemesX with only a knife.
The Knifedodge is extremely useful, but his attacks are to put it nicely really, really hard to time right. And there's a good chance it won't really even get in, because the Knifedodge usually only hits his lower chest, not his heart. You probably want to take a couple stabs at his heart before performing a Knifedodge, if you can. Above all else make sure there are no other zombies. You're fighting undead Andre the Giant in his prime and you don't need chompers biting at you while Nemesis is giving it to you.
I highly recommend this video to give you insight on how the hell you even attempt this. Learn the patterns, learn his actions, and above all else, please have healing items.