Unsigned book that is known as unsigned6_unknown.md was found in the Nether at -863 / 22 / -175 on mc.tildeverse.org.
Here's a short guide on how to grind for XP efficiently. There should be plenty of stone swords in the chest where you got this book (if you're copying this book to place it elsewhere please put a bunch of stone swords in the chest with it), and this is for one simple reason:
Mending is a wonderful enchant and I'm glad it exists. Here's how to most effectively utilize Mending with an XP grinder.
If you aren't attempting to repair any Mending gear, TAKE IT OFF. That way, all of the XP from the grinder goes right into your XP bar and
none of it is wasted on mending your gear. This is why the stone swords are here: they work just as fine in the grinder as your Diamond or Netherite Mending sword would, and they don't have any enchants on them.
If you are attempting to mend some gear, though, I would
suggest taking off any fully-repaired Mending gear. I'm not sure if they fixed this, but I remember in previous versions the game wouldn't correctly distribute the XP if some Mending gear was on but fully repaired. Even if it's just superstition, why risk it?
Anyways, that's my tips on how to grind efficiently.