Discerner
DISCERNER, noun
1. One who sees, discovers or distinguishes; an observer.
2. One who knows and judges; one who has the power of distinguishing.
He was a great observer and discerner of mens natures and humors.
3. That which distinguishes; or that which causes to understand.
The word of God is quick and powerful--a discerner of the thoughts and intents of the heart. Hebrews 4:12.