The .nxs file is in XML format. It contains user readable keys which names are intended to be self-explanatory.
To see how the .nxs file looks like, please open any of the connection files created from the NoMachine GUI. They are stored in the directory specified for Connections in the Player settings. For example on Windows, the .nxs files are stored by default here: %USERPROFILE%\Documents\NoMachine