I'm guessing it's for your wireless? If you forgot it, connect to the router setup, go into the wireless config page and change it. You'll have to reconnect anything else connected though wifi.
The network password is made when you set it up and make a homegroup. To get that password so that your ipod can join the homegroup you can go into the Control panel / Network and Internet / Homegroup / View and Print your Homegroup Password. Naturaly you don't need to print it but you casn see it.
1)Open the web browser that you use: Firefox,Google Chrome,IE,or Opera and type in the IP address for your router,and press the Enter key.
http://www.routeripaddress.com/ < Router ip addresses can be found here
2)A window will open and then type in your routers default username and password,and press the Enter key again
http://www.routerpasswords.com/ < Router usernames and passwords found here ***** Username and Password may also be located on the side or bottom of your router *****
3)Navigate to the Wireless Security\Network Security Settings Tab and open to locate or change your WEP or WPA Security Passphrase. Use WPA because it provides better security.
4)Write this Security Passphrase down and put it in a safe place to access when needed.