Assuming you mean the commandline server ‘openssl s_server’
(there are lots of other things that could be described as ‘openssl server’):
man s_server or http://www.openssl.org/docs/apps/s_server.html#CONNECTED_COMMANDS
except just now when I tried to confirm I got flaky DNS results so if necessary use 185.9.166.106 .
Although I notice that the manpage says ‘neither –www nor –WWW’ but the code also disables
this logic if –quiet (apparently because this is considered ‘session’ output?).
In what way is the s_server documentation page "for the openssl s_client"?
You can exit s_server by sending it a command over a connection from any client, as described in the s_server documentation section which Dave linked to below; or you can use any ordinary local method to kill the s_server process (such as hitting control-c in common configurations on many OSes).
What problem are you trying to solve? Why would typing Shift-Q on the keyboard be acceptable when typing Ctrl-C isn't?