See iTunes music track in the Dock in OS X
See popup iTunes track in the Dock on your Mac
Here's how you can see a popup in the Dock when iTunes starts playing a new song.
1. Open a terminal window.
2. Type in the following command, then hit Enter.
defaults write com.apple.dock notification-always-show-image -bool TRUE; killall Dock
3. You can deactivate it using these commands:
defaults delete com.apple.dock itunes-notifications
defaults delete com.apple.dock notification-always-show-image;killall Dock
For more, see the original article at the link below.
See the iTunes Track in the Dock | Amsys