If you have the create Enchantment Industries mod. go to this schematic that has a killing an xp collection system.
https://createmod.com/schematics/silverfish-xp-farm-with-killing-and-collection-system

Today I'm showing you a compact and quick Create mod XP farm that uses a cobblestone generator to make silverfish. The farm has a built-in XP farming system and a "build your own" style if that suits your world better. This farm can get you to level 30 in 15 seconds and produces ~750,000 mB of XP per hour (256 levels). The farm fits in an 8x8x10 space and can be expanded if necessary.