You can get the serial number for iPod/iPhone/iPad devices you've plugged into your Mac with iTunes from the file
For more info on opening
plist (Property List) files, see How do I open a .plist file?
com.apple.iPod.plist, the Plist structure has a Dictionary of Devices, with each device listed separately under that, using a unique hex string (something like
4223F0FD7A331BA1), under that you'll see useful information like:
- Device Class (e.g. iPod)
- Connected (last date iTunes connected to the device)
- Family ID (Apple's code for a specific family of device models)
- Serial Number
The first few should let you figure out exactly which one is the iPod you think your friend has stolen. The last 3 digits of the Serial Number specify the device model, so you can differentiate some of them based on this advice if there are multiple iPods listed. The Serial Number of course cannot be changed so identifies the specific device.
It's not entirely clear from your question how you're seeing the device in your iTunes, but presumably it is on the same wifi network or something? If your iTunes has connected to both yours and his iPod (which you allege to be the same device), then you should be able to check whether it is indeed the same device by looking at this list of devices. I'm not sure if this list is updated for devices seen on the wifi network or not though, or whether its only for devices that actually sync.
You should be able to tell fairly easily if his iPod is in the list though by checking the 'Connected' dates on any iPod devices in the list.
If its a different device (and if your
com.apple.iPod.plist file hasn't been cleared since you lost your iPod), then there'll be a separate entry for each. For example, another iPod in the list that was last connected around the date you lost yours, along side his new iPod... If its the same device, then it'll only have one entry, so your old one won't be shown separately, and you will see the Serial Number there, with a recent 'Connected' date. However this isn't exactly proof since its still possible your old iPod is simply not listed for some reason.
If your friend's iPod isn't showing up in the list (based on recent Connected dates), then you can hopefully at least get the serial number of your iPod from this list (again, if it's not been cleared for some reason). You can then compare it to the serial number of his iPod to check if it's the same. Here is some info about getting serial numbers off iPods.