if Windows Serer 2012 (R2) is configured in RDP Administration mode, which is the default, it is no more possible to connect to a other users remote desktop session with the GUI “Remote Desktop Services Manager”. Microsoft has removed this tool and do not provide an equivalent replacement.
But its still possible from a console window 🙂 Open a cmd shell and list all sessions.
C:\> qwinsta SESSIONNAME USERNAME ID STATE TYPE DEVICE services 0 Disc >rdp-tcp#88 USER 1 Active rdp-tcp#89 UserTOControl 2 Active console 3 Conn rdp-tcp 65536 Listen
In this example USER is the one who wants to connect to the session of UserTOControl. Both are connect through a RDP session (not at the console).
To connect to the session start the Remote Desktop Client with the shadow parameter followed by the session ID you want to connect to. UserTOControl has to accept the incoming request.
C:\> mstsc /shadow:2
C:\> tscon 2