ls -a /tmp/.X11-unix
ps axu | grep -iE '(nx|x2goagent)'

Naturally on the server side.

ls -a /tmp/.X11-unix
.  ..  X0


Let's try something more low-level. Connect to the machine via ssh -X.

nxagent :23 & [you should see an empty/black nxagent window after issuing this
command]

nxagent :23 &
[1] 9992
[kudyba@sobolev ~]$ 
NXAGENT - Version 3.5.99.7

Copyright (c) 2001, 2011 NoMachine (http://www.nomachine.com)
Copyright (c) 2008-2014 Oleksandr Shneyder <o.shneyder@phoca-gmbh.de>
Copyright (c) 2011-2016 Mike Gabriel <mike.gabriel@das-netzwerkteam.de>
Copyright (c) 2014-2016 Ulrich Sibiller <uli42@gmx.de>
Copyright (c) 2014-2016 Mihai Moldovan <ionic@ionic.de>
Copyright (c) 2015-2016 Qindel Group (http://www.qindel.com)
See https://github.com/ArcticaProject/nx-libs for more information.

Info: Agent running with pid '9992'.
Session: Starting session at 'Wed Nov  1 09:26:08 2017'.
Info: Using alpha channel in render extension.
Info: Not using local device configuration changes.
Info: Using builtin keystrokes.
Current known keystrokes:
  close_session         Ctrl+Alt+t
  switch_all_screens    Ctrl+Alt+f
  fullscreen            Ctrl+Shift+Alt+f
  minimize              Ctrl+Alt+m
  defer                 Ctrl+Alt+e
  ignore                Ctrl+Alt+BackSpace
  ignore                Terminate_Server
  force_synchronization Ctrl+Alt+j
  resize                Ctrl+Alt+r
  viewport_move_left    Ctrl+Shift+Alt+Left
  viewport_move_left    Ctrl+Shift+Alt+KP_Left
  viewport_move_up      Ctrl+Shift+Alt+Up
  viewport_move_up      Ctrl+Shift+Alt+KP_Up
  viewport_move_right   Ctrl+Shift+Alt+Right
  viewport_move_right   Ctrl+Shift+Alt+KP_Right
  viewport_move_down    Ctrl+Shift+Alt+Down
  viewport_move_down    Ctrl+Shift+Alt+KP_Down
  viewport_scroll_left  Ctrl+Alt+Left
  viewport_scroll_left  Ctrl+Alt+KP_Left
  viewport_scroll_up    Ctrl+Alt+Up
  viewport_scroll_up    Ctrl+Alt+KP_Up
  viewport_scroll_right Ctrl+Alt+Right
  viewport_scroll_right Ctrl+Alt+KP_Right
  viewport_scroll_down  Ctrl+Alt+Down
  viewport_scroll_down  Ctrl+Alt+KP_Down
  reread_keystrokes     Ctrl+Alt+k
error opening security policy file /usr/lib64/xserver/SecurityPolicy
SessionPath not defined
Session: Session started at 'Wed Nov  1 09:26:13 2017'.
Info: Screen [0] resized to geometry [1440x793] fullscreen [0].


xauth list
xauth add :23 . "$(mcookie)"
xauth list
xauth remove :23
kill $!

Here you go hope there’s something helpful:
 xauth 
Using authority file /u/erdos/myuser/.Xauthority
xauth> xauth add :23 . "$(mcookie)"
xauth: (stdin):1:  unknown command "xauth"
xauth> xauth list
xauth: (stdin):2:  unknown command "xauth"
xauth> quit
[myuser@myworkstation ~]$ xauth add :23 . "$(mcookie)"
[myuser@myworkstation ~]$ xauth list
erdos.sub.ourshool.edu/unix:0  MIT-MAGIC-COOKIE-1  dfae2f651992831ac371ed79e246969d
myworkstation/unix:135  MIT-MAGIC-COOKIE-1  a07673b2f4a6762816b74954bb7c4d08
myworkstation.dsm.ourshool.edu:135  MIT-MAGIC-COOKIE-1  a07673b2f4a6762816b74954bb7c4d08
erdos/unix:222  MIT-MAGIC-COOKIE-1  c2e600da0e177cd41f5ac4325267fc02
erdos.sub.ourshool.edu/unix:222  MIT-MAGIC-COOKIE-1  c2e600da0e177cd41f5ac4325267fc02
myworkstation/unix:141  MIT-MAGIC-COOKIE-1  6491ffce94620e7009a1e89858326a9c
myworkstation.sub.ourshool.edu:141  MIT-MAGIC-COOKIE-1  6491ffce94620e7009a1e89858326a9c
myworkstation/unix:143  MIT-MAGIC-COOKIE-1  0e851008661538233db64a10868ce953
myworkstation.sub.ourshool.edu:143  MIT-MAGIC-COOKIE-1  0e851008661538233db64a10868ce953
myworkstation/unix:144  MIT-MAGIC-COOKIE-1  e9221e75a72dde8abb668e08396b043a
myworkstation.sub.ourshool.edu:144  MIT-MAGIC-COOKIE-1  e9221e75a72dde8abb668e08396b043a
dsm.sub.ourshool.edu/unix:10  MIT-MAGIC-COOKIE-1  1862bc203e0f1f39d6f06dca384dc134
kopernik.sub.ourshool.edu/unix:10  MIT-MAGIC-COOKIE-1  4cb123498718884f4e5b2f3dc91e2c97
dsm.sub.ourshool.edu/unix:11  MIT-MAGIC-COOKIE-1  e66b6650e7a0f315f9b58f1649de332c
myworkstation.sub.ourshool.edu/unix:10  MIT-MAGIC-COOKIE-1  78040df9ea9c3825e6bfa886c9bf27e1
myworkstation.sub.ourshool.edu/unix:23  MIT-MAGIC-COOKIE-1  aa0dd8187b5ed170fc8b10c5f6953c96
[myuser@myworkstation ~]$ xauth remove :23
[myuser@myworkstation ~]$ kill $!
Session: Terminating session at 'Wed Nov  1 09:28:08 2017'.
Session: Session terminated at 'Wed Nov  1 09:28:08 2017'.
[myuser@myworkstation ~]$ FreeFontPath: FPE "/usr/share/nx/fonts/misc/" refcount is 2, should be 1; fixing.

[1]+  Done                    nxagent :23