The idea behind Knights and Knaves Cards is that information from Knights is always true and information from Knaves is always false. There are thousands of puzzles and related discussions about statements made by Knights and Knaves.
I imagine card games where the Back of the card is identical to the Front, so other players can see what the other players have. These are Knight cards. They always tell the truth. But only about half of the cards are this way. The other half shows one image on the Back but the actual value of the card, on the Front, is another. These are Knave cards. They always lie.
The idea is to produce the decks and let players choose their favorite games, whatever games they choose.
The deal is made from a deck of 104 cards, 52 for Knights where the Front and Back match, and 52 where the Front is one thing and the Back is another. The number of cards dealt depends on the game played. We don't know how many of our cards are from the Knights' deck or how many cards are from Knaves' deck; they have been merged and shuffled together.
Here is an example of the Knight version of the four of Spades. The Back is what other players see and the Front side is viewed by the player holding the card.