According to the Sony PlayStation website, the enter button on the PS3 media remote can be found in the center of the device. The PlayStation site includes an image of the remote that shows the enter button.
The "X" button, located to the lower right of the button marked enter, usually functions as the enter button when the PS3 media remote is used to navigate menus on the console. Most menus include a legend at the bottom right corner of the screen with information on button functionality. The PlayStation website also offers information on common controller functions for different activities on the console. The online Knowledge Center provides outlines of several common controller functions and a search bar to quickly navigate through questions and answers.