I forgot my screen unlock combination code of iPod Nano 8GB. Is there any master combination code to reset the screen lock code?

There isn't one. If you cannot remember the passcode, you'll have to connect the iPod to iTunes and restore it to factory settings.

Restoring iPod to factory settings

B-rock

Hey,

If you still have the original computer that you synced that iPod to, all you have to do is connect it, then sync it and then disconnect from iTunes. It should be unlocked, as I have had to do this many times before.

Hope this helps