ידע yd` a common verb with a wide range of uses, most related to the knowledge and skill that can be gained by the senses. It is used of God's knowing (anthropomorphism?).
In Amos God "knows" Israel in the sense of having a close relationship with them (3:2) but also knows their rebellious nature (5:12).
Israel, by contrast does not "know" how to act rightly (3:10).
The participle, "knowers", is used of those "skilled" as mourners (5:16).