First option — use command line to
query user /server:SERVERNAME (or
quser.exe - same thing). This shows User name, Session name, Session Id, Session state, Idle Time and Logon Time for all logged in users.
Second option — use command line to
query session /server:SERVERNAME. This shows User name, Session name, Session ID and Session state. It shows all sessions, including disconnected ones, which might be useful.
Third option — install Microsoft Remote Desktop Connection Manager, configure your server(s), then right-click on the server to "list sessions". This shows Session ID, Session state, User domain/name, client machine name. Note that
qsession don't show client machine name, which might be useful to identify who is actually using the machine. RDCM doesn't show idle/logon time though, and it's quite outdated and glitchy.
Also important to note that all methods will fail to show active sessions if current user does not have admin rights on the queried remote server. So use
runas /u:DOMAIN\adminUser cmd.exe to start admin console first.