There isn't a way to recover a forgotten iPod password, as of November 2015. However, you can reset the iPod using iTunes, iCloud or recovery mode. Resetting deletes the iPod's data and settings.
If you have previously synced the iPod with iTunes, connect it to the computer you synced with, and launch iTunes. If iTunes asks you for a password, use another computer you've previously synced with. If iTunes doesn't automatically sync the iPod, click the Sync button. Click Restore iPod, select Restore From iTunes Backup when you reach the setup screen, and choose an appropriate backup to restore.
If you had previously set up Find My iPhone on the iPod, you can use iCloud to restore it. Log in to your iCloud account, click All Devices, select your iPod and click Erase iPod. You may then restore the iPod from a backup or set it up as a new device.
To erase the iPod from recovery mode, first connect it to a computer, and open iTunes. While connected, press and hold the Sleep and the Home buttons at the same time until you see the Recovery Mode screen. When you see the Restore and Update options in iTunes, click Restore. Wait for the process to finish, and then set up the iPod.