Looks like a few dead or dying pixels on your iPod's LCD screen. If none the usual 5 R's of troubleshooting resolve the issue, your iPod will need servicing.
How much it costs depends on where and who services the iPod. Here is Apple's pricing.
It would be cheaper to send it to a third party repair center. Google for "ipod classic screen replacement" and you should get a plethora of results to work with.
The last option would be to find a parts reseller and purchase a new screen from them and then swap it out yourself using instruction guides/videos found online.