How do you get a knight on valhalla knights?

I've been looking things up and it said you must kill greater demons to get a knight card.

If you are referring to Valhalla Knights : Eldar Saga, I can help you out as I have played this game ALOT. If you're referring to VK 1 or 2, I cannot help you.

For VKES, you simply need too complete the first optional quests in Episode 2 to get the Knight Card. For the other games, I hope someone else reads this and can answer.