The key combination varies with each language settings. Make sure your language settings are set to English (United States) and you should be able to open the console by pressing the ~ in the upper left corner of your keyboard. Note that in Kotor 2, the console is invisible. Also make sure you capitalize the E and the C in
Instead of the console, you can also use KSE (you can do much more than with cheats) and there is no need to bother with the console.
KSE is on this page: http://starwarsknights.com/tools.php