How do I separate enchants from items?
Unfortunately, you can't. You can remove enchantments from items in 1.14 by using the grindstone, but you won't be able to put it in a book: it will just de-enchant the item and you will get some experience.
This isn't currently possible in vanilla Minecraft. However, there do exist mods that will let you do this (which will require Forge). One such mod is The Disenchanter Mod.