Unless you know how to copy songs between iPod and PC.
Otherwise, take this guide: How to Transfer Music from iPod touch to Computer

Hope this works, too. It's about 3 Ways to transfer music from iPod to iTunes library.

Syncing iPod with iTunes is really quite easy. Gather your iPod and its USB charging cable, and make sure you have installed the latest version of iTunes on PC/Mac. Plug in your device, and iTunes should launch, displaying your device’s summary screen. The guidance below will show you the further steps.

1. Open iTunes. Make sure that you have the latest version. Then connect your iPod with USB cable to your computer.

2. Click on your device. After clicking on your device, tabs appear on the left side of the iTunes window under Settings.

3. Turn on syncing. You can turn on syncing for Music, Movies, TV Shows, Podcasts, Books, Audiobooks, Tones, Photos, and Info.

4. Sync your content. Click the Sync button in the lower-right corner of the screen to sync your content.