I have a node red application which collects information from various cobots and PLC's from production lines.
I would like to roll out this application to more production lines, so how can I know how much space a pc required to run the node red and UI.
What sort of space do you mean?
storage of application and to run it.
Any modern PC will have more than enough disc and RAM to easily run node-red. It can even run on a Pi Zero with 0.5 MB RAM and 4MB SD card.
If you also want to run the browser on the PC that that will need vastly more resources than node-red.
Presumably you have a test system so you will already know better than we what storage space is required. We don't know what extra things you might have installed, the OS, whether you have any databases or data files, whether you need on-device backups, ...........