Connoisseur

Connoisseur: A person well versed in any subject; a skillful or knowing person; a critical judge or master of any art, particularly of painting and sculpture.

From French connaisseur.  The French word derives from the verb connoître (acquainted, to know).  Father of the modern French verb is the Old French verb conoistre, itself from Latin cognosco (I know). 

Cognosco comes from the Latin word con (with) and the Greek word γιγνώσκω (gignosko) meaning, I know.