You can find that in the Real Time Monitoring Tool, but you probably would not give that to the Attendants if you goal is to have them aware of currently logged in resources.
From the RTMT Admin Guide:
ClientsOnline This counter represents the total number of Cisco Unified Communications
Manager attendant console clients that are currently online. Attendant Console
clients include all users that are configured in the attendant console User
Configuration window in Cisco Unified Communications Manager
Administration that are currently online. This number increases by one for each
client that goes online and decreases by one for each client that goes offline.