Assess Creature

Source: VM Guide to the Planes

You gain insight into the capabilities of one creature within range. The target must attempt an Intelligence saving throw. On a successful save, the creature becomes aware that it was a target of a spell and the spells ends, revealing no useful information. On a failed save, you learn the target's current hit points, armor class, or which saving throw it has proficiency in. In addition, you learn if it is a spellcaster and which ability score it uses to cast spells. 

At Higher Levels

When you cast this spell using a spell slot of 4th level or higher, you also learn one of the target's ability scores (your choice). When you cast this spell at a 6th level or higher, the target is unaware that it was the target of this spell, even on a successful save.