Yukabacera
Idyr of the dead
Seriously? It's on the back of your 3DS. It's the little white strip. Unless you installed the Nyko extended life battery. Then you'll have to find your original back-plate.
Seriously? That's the serial number.
Oh you mean the piece of paper that comes with the game that has a code that you enter on the Nintendo Website to get surveys for coins. if you have lost that then you'll have to buy the game again in order to redeem a new code. them's the breaks, but having to do that is kinda lame. the best thing to do is when you get a new game with a code like that, write it down on a piece of paper and put it in a place where you can find it, then when you get the chance to redeem it and you've lost the original you can refer to the backup.