Visionary (5e Feat)
From D&D Wiki
Each time you make a weapon attack against an enemy, you gain a charge, up to a maximum of 10. You lose all charges upon completing a short or long rest. You may expend 10 charges to gain knowledge about one of the following aspects of a creature:
- Resistances the creature has.
- Immunities the creature has.
- Damage types the creature can inflict with weapons they possess, and spells they can cast.