dtlogin, like XDM (X Display Manager) on which it is based, uses the Xservers file to specify how the local Xserver is started. By default, the last line in this file is:
:0 Local local@console /usr/openwin/bin/Xsun :0
:0 means that the Xserver display is <localhost:0>.
Replace local with foreign if you want to attach to a running X11 server.
/usr/openwin/bin/Xsun is the path to the X11 server.
The Solaris CDE and OpenWindowsTM environments run the same X11 server.
Refer to the dtlogin(1) man page for more information about this file. You can also review the explanatory comments in the file itself.