How do I check the effective file permissions/accessibilty for/of a given file and a given user?
One commercial app which provides the effective permissions for a user and a selected file or folder is TinkerTool System:

In the example below the effective permissions of the file /private/var/log/clamav.log for the user Spotlight are shown. The user Spotlight can neither read nor write data.



Triggering the tab Show or Set Permissions the POSIX permissions/ownership are shown explicitly.