As far as I know, it's not currently possible to block PWAs specifically with Netskope.
At the proxy level, there's no header or field in the request that indicates it came from a PWA.
At the process level, PWAs run inside chrome.exe, so from Netskope's perspective the traffic looks like a regular Chrome session.
If you're managing Chrome via Enterprise policies, you can restrict PWA installation there. Note that blocking the domain in Netskope will block the site in both a standard chrome tab and a PWA.
That said, I'd confirm with Netskope support via a How-To ticket in case there's something newer I'm not aware of.