The adjective discerning means someone who can judge well if something of a particular kind is good or bad.

Synonyms are insightful, knowledgeable, knowing, or astute.

The word origins from 1600, present-participle adjective from discern in the sense “discover by the intellect, understand”.

I admire his discerning instinct.

He is a discerning reader.

We trust his discerning eye to pick the right candidate for us.