A Challenge Point is an in-game resource that is consumed each time a player initiates a PVP battle. Practice sessions do not consume Challenge Points.
Challenge Points are tracked on the Challenge Bar, which has a maximum of 5 Challenge Points. The Challenge Bar is refilled at a rate of 1 Challenge Point every thirty minutes, or 5 Challenge Points per two hours. It does not refill when the agent levels up.
Challenge Points can also be obtained from certain links provided in the game's Facebook App Page, which can be accessed from the wiki's free items page for Facebook players.
They can be bought in the Store under Energy. They cannot be sold.