You attempt to reverse the effect of a Divination spell upon its caster.

When you are aware of being the target of a Divination spell, or aware of a sensor created by a Divination spell, you can cast this spell. The Divination spell that you are aware of automatically ends if it is of 7th-Level or lower; otherwise, this spell fails.

If this spell succeeds, then if you were targeted by a Divination spell, you can automatically cast the associated spell targeted against the original caster as part of this reaction, regardless of distance. If this spell was used in response to a divination sensor, you can automatically cast the Scrying spell against the original caster as part of this reaction. In either case, the target has Disadvantage on any Saving Throw made on any spell you cast on them as part of this spell. Furthermore, you become immune to any effect that would sense your emotions or read your thoughts, as well as any divination effects, for 24 hours.

(For example, if you were the target of the 5th-Level Scrying spell and were able to see the Invisible sensor via an effect like the spell Piercing Sight, then you could use this spell to negate that spell, and cast Scrying back upon the caster, even if you do not necessarily know who it was. They would still have the appropriate modifiers to their spell save DC as part of Scrying.

Or perhaps you have cast the 1st-Level Detect Magick spell, and can see traces of divination school magick; You could target that effect.)