Instructions
Click on the small notepad icon on the top right corner of the touch screen. A keypad will appear.
Type in the word "knight." Even if you misspell it, Scribblenauts will suggest the correct spelling. When you are done, hit the "Enter" key.
The knight will appear in several seconds, complete with a suit of armor. At first, he will be red. Use the stylus to place him on solid ground. When he turns green you can lift the stylus, and the knight will start attacking nearby enemies or following the game's hero around.