While streaming, you can use your Artist Panel to see how many users are currently watching your stream.
This can be done by clicking the small “eye” icon found over your video feed, just above your chat room - clicking that icon will display the number of users currently present in your live stream room.

At the moment, it’s not possible to see a descriptive list of the usernames of the people that are present in your room - just the total number of current viewers.