Count total amount of sessions/connections open on Documentum Content Server

You'll find this information on the DQL Reference, here is an excerpt of it:

root_start             The time when the main server thread (root server process) was started
root_pid                On Windows, the process ID of the Content Server process.
                             On UNIX, the process ID of the root Content Server process.
shared_mem_id    The ID of the shared memory segment used by the servers.
                              This property is returned only on UNIX platforms.
semaphore_id        The ID of the semaphore used by the servers.
                              This property is returned only on UNIX platforms.
session                  The object ID of the session begun by user_name.
db_session_id       The ID of the database session.
typelockdb_session_id  The database session ID for type locking
tempdb_session_ids List of temporary database sessions
pid                           The ID of the session thread (process).
user_name             The user name of the user who started the session.
user_authentication The user authentication state for the session. Possible values are password,
                                  ticket, trusted client, change password, or in progress.
                                  If the value is change password, the user logged in for that session can only
                                  perform the change password operation. No other operations are allowed.
client_host               The host name of the machine on which the session was started.
client_lib_ver          The version number of the DFC in use for the session.
client_locale             A verbose description of the clients environment, including the operating
                                 system version, the character set in use,the language in use, and the date format.
                                 start The starting time of the session.
last_used                The last time the client session contacted the server.
session_status       The session status. Active means that the session is connected and has not timed
                                out. Inactive means that the session has timed out.
shutdown_flag         Records the setting of the immediacy_level argument in the kill method.
last_rpc                    The last RPC the server ran for the session
                                 current_rpc The current RPC being run by the server for the session
                               Note that after the RPC is completed the server will not clear this field. Therefore,
                                if last_rpc and current_rpc have the same value, either the server has completed an
                               RPC for the session and has not executed another RPC, or the server is running the
                               same RPC again.
last_completed_rpc The last time theserver completed an RPC for the session