The Xev utility helps to analyze keyboard and mouse events: https://www.x.org/archive/X11R7.7/doc/man/man1/xev.1.xhtml

How to use it with NoMachine:

1) Connect to the NoMachine desktop. 

2) Reproduce the keyboard or mouse problem (e.g. an incorrect key mapping etc ...)

3) Open a terminal and launch the xev tool from command line and redirect its output to a file:

xev > xev.out

The Xev tool will open the 'Event Tester' window with a small square inside.

Note: if you cannot type the command due to keyboard problems, copy and paste it in the terminal.

4) Focus on the 'Event Tester' window (you can even maximize it) and repeat the key press sequence or the mouse event to reproduce the the issue. You will not see any output while making the test.

5) Once done, close the 'Event Tester' window.

6) Send the xev.out file to the Support Team