well, like with most any ServiceNow table, you can examine it by going to the filter at the top of the sidebar and entering the tablename followed by ".list" ... don't press ENTER when you're done.
Just enter: sys_user_has_role.list
... and you'll get the list of all pairings of user and role. Obviously you can only do this as an administrator. Well, you can still perform the search, but most (often ALL) of the records will be invisible to a non-administrator.
