Sorry, I see no logs in /usr/NX/var/log.
I only see logs in /var/log and nothing for NoMachine nor NX?
ubuntu@ubuntu:/var/log$ ls
alternatives.log auth.log.3.gz dmesg hp syslog.1
alternatives.log.1 auth.log.4.gz dmesg.0 installer syslog.2.gz
anydesk.trace boot.log dmesg.1.gz journal syslog.3.gz
apport.log boot.log.1 dmesg.2.gz kern.log syslog.4.gz
apport.log.1 boot.log.2 dmesg.3.gz kern.log.1 ubuntu-advantage.log
apport.log.2.gz boot.log.3 dmesg.4.gz kern.log.2.gz ubuntu-advantage.log.1
apport.log.3.gz boot.log.4 dpkg.log kern.log.3.gz unattended-upgrades
apport.log.4.gz boot.log.5 dpkg.log.1 kern.log.4.gz wtmp
apport.log.5.gz boot.log.6 faillog lastlog Xorg.0.log
apport.log.6.gz bootstrap.log fontconfig.log libvirt Xorg.0.log.old
apt btmp gdm3 openvpn Xorg.1.log
auth.log btmp.1 gpu-manager.log private Xorg.1.log.old
auth.log.1 cups gpu-manager-switch.log speech-dispatcher
auth.log.2.gz dist-upgrade helpdesk syslog