In Dead Rising 2 for the PS3, Xbox 360, and PC, part of the Knights Armor is worn by a simple minded survivor named Jack. In order to get the helmet from him, you’ll need to beat him at strip poker.
First you’ll need to make sure you saved Jack in the mission “Welcome to the Family”. After that, around day three you’ll receive a side mission called “Ante Up”. Save the game before you start just in case, but Jack should join your game if he is in your safe house.
Beat Jack to take his Knights Helmet.