Is the questioner sinful for telling his colleague the name of a song he saw in a YouTube clip, and is listening to songs forbidden in Islamic law?

Some singing is permissible, but most of what is available is forbidden. If what your colleague is requesting is of the forbidden type, then it is not permissible for you to listen to it, nor to assist or direct anyone to listen to it; for that entails cooperation in sin and aggression, which is forbidden by Islamic law.