Wanted to just update on here, for anyone else who might be having the same issue(s)

The port list above, is correct and works - with regards to what is needed on the Private App config for the print server.

What was missing (and not an issue with Netskope itself) was on our print server, we needed to configure the print jobs to be rendered on the server and not on the client computers.

Once we did that, users were able to print now.

Are you using IP addresses in the Private Apps?  If so, is the user mapped to the printer via IP or a print server?

In most cases, we use both hostnames and IPs.

Try mapping the printer via the IP.  Also, have the user run an NSLOOKUP on the FQDN for the printer to see if its coming back with a 191.1.x.x IP or a 100.64.0.0/16 range if you changed the GNAT range.  This will tell you if its being steered by NPA.  I do know you wont be able to access the printer via the Web interface, HP, Xerox, Rhino and a few others do not like it when Netskope tries to steer the traffic but you should still be able to print.  If you try to ping the actual IP assigned to the printer it should fail but come back with the GNAT IP if its being steered by NPA.  This will help troubleshoot your issue. Let me know your results.