To connect over internet you have to enable UPnP or open port manually in the router settings. Please refer https://www.nomachine.com/AR11L00827. In the article you have instruction how to enable UPnP in the NoMachine server.
Check also https://www.nomachine.com/getting-started-with-nomachine – section: Using NoMachine for remote access to a computer over the internet.
If you want forward port manually you should pass traffic to port 4000 (NX protocol), 22 (SSH protocol on Linux/MacOSX) or (4022) (SSH protocol on Windows). Follow the router instruction to know how to do that (guide you can also find in the internet, for example from there: https://portforward.com/netgear/wndr3700/).