what is a pin for the dsi xl
The serial number is on the back of the DSi XL. If that code has worn of, open the battery cover. There should be another serial code under the battery.
Another code is on a club Nintendo packet. That should be in the box the DSi XL came in with.
He's probably talking about the parental controls PIN.
If you are trying to access something on your DSiXL, and it asks you for a 4 digit PIN, then parental controls are turned on. If you forgot your PIN or don't know it because you bought a used system, you will have to contact Nintendo at 1-800-255-3700, and they will tell you how to reset the PIN.