You don't hear about knaves much these days: it's an older word for a rascal, a scoundrel, or a rogue. It isn't a compliment.
If you read Shakespeare for long, you'll definitely see the word knave more than once. In Shakespeare, an important person like a king or a prince might call a thief a knave. Knaves always tend to be up to trouble. You don't want to trust a knave; knaves lie, deceive, and betray. Today, we might call a knave a "scoundrel" or a "good-for-nothing."