Since you're accessing a UNC path, you don't have to worry about mapping.
The first thing you should then do is make sure that the qubeproxy user can access the share without requiring an authentication. You should be able to login as qubeproxy on the Worker host, and then access the path to your scenefile using something like Windows Explorer. It should work without requiring a password.
Once you can do that, you should be able to test this by submitting this command line job:
dir \\fileserver\3dshare\Projects\Default\scenes\Can.mb
More information about how the qubeproxy user works can be found in the Post-installation chapter of the Installation manual.
