The rabbitmqctl command with the list_user_permissions option can be used to list a users permissions. In this example, John Doe's permission will be listed.
rabbitmqctl list_user_permissions john.doe
If something like this is returned, this means John Doe has not been granted permission to any virtual hosts. In this scenarion, you'll probably want to use the set_permissions option to update John Doe's account to have certain permissions to certain objects.
Listing permissions for user "john.doe"
On the other hand, if the user has permission, something like this should be returned. In this example, John Doe has the following permissions:
Listing permissions for user "john.doe" / .* .* .*
The --formatter json option can be used to return the output in JSON.
rabbitmqctl list_permissions --formatter json