NPrinting can be installed on the same server as publisher.
NPrinting requires the QV desktop to run reports where ever QVWs are located including with the NPrinting server. Therefore the answer is yes, the QV desktop requires a licensed QV client.
NPrinting sends it's API calls to the QV desktop so therefore, the QV desktop must be licensed as NPrinting does not work with QV personal edition.
To ensure you have a fully configured, healthy NPrinting Environment, please check the documentation at the link below: