on most vehicles theyre are tons of codes in the trunk on a sticker usually posted underneath side of what hides your spare tire. however you kind of have to know what you are looking for because it wont say what code is what. all your codes are under theyre paint code, lock code, etc etc. maybe also check the sticker inside the drivers side door.
The keycode is usually written in the manual. Check the manual if you have it, if not you will have to call an actual Nissan dealership. Just be sure to have your vin# handy.