Enlightening Spell
Spend 1 sorcery point to learn a target's resistance or immunity.
When you cast a spell that targets a creature, you can spend 1 sorcery point to learn one of your target’s resistances or immunities. Each time you use this metamagic option on the same creature, it reveals a new resistance or immunity.
Source and licence
From Tome of Heroes.
Licence: Open Game Content (OGL 1.0a).