Surface Go Tablet is a touch screen tablet with no peripherals attached. It provides a touch keyboard which opens when a text field is selected.

However, not all applications, included the NoMachine client, are allowed by default to open the virtual keyboard when an input field gets focused.

Change Windows settings in Settings -> Devices -> Typing (or similar, this depend on the Windows 10 version) and ensure that the following option is checked:

"Automatically show the touch keyboard in windowed apps when there's no keyboard attached to your device"