If you are connecting to your co-worker's or friend's machine and using the target machine's IP address all you need is the NoMachine Player installed on your device. It is the person responsible for the target machine which must make sure that the software installed has been activated with the appropriate software license.  You do not need a software subscription to connect to someone else's computer over IP.

The NoMachine Player (aka Enterprise Client) or the NoMachine mobile applications are free to install and use. They can be downloaded from: https://download.nomachine.com.

Instead, if you want to connect to the target machine using the NoMachine Network service, so using its Machine Id, you will need to acquire a NoMachine Network subscription. When you open the NoMachine Player on the local device, login with your User Id in the UI and insert the Machine Id instead of the IP to start your connection.