The correct answer to this open question is the following.
Although there are no options attached we can say the following.
The listening function that would be most appropriate for you to practice if your shyest friend decided to sing a song at your local karaoke bar is the function of listening to support.
In this case, you know that your friend is so shy, that it is so hard for him to be in public places or being the central figure of an event or conversation. And in this case, he is about to sign in public. He is going to get on a stage and sing a song in front of many people.
That is why it is so important to show your total support to give him confidence and not hurt his feelings.
