You can see which users are currently online (logged in) in your Domo instance. This is shown in the Discover pane in Buzz, in the "Online Now" section.
Profile pictures for the 5 users you interact with the most appear here, but you can see a list of all online users by clicking View All.
In this list, a green dot indicates the user has been active in Domo within the last 10 minutes, whereas a yellow dot indicates they have been idle for the last 10 minutes.
You can search for specific users in this list by entering their names into the Search field at the top of the pane.