The iPod manager tool, iTunes allows only to copy your music TO the iPod. However if you would like to get the music off (e.g. migrating to another MP3 player) or simply want to backup it’s storage, you can use the following FREE apps:
DeTune (Recommended)
iPodDisk

For more information: http://www.metaphoriclabs.com/articles/5-ways-to-copy-music-off-your-ipod-windows-mac-os-x/