You can then simply use the attribute_view_gui to display the list
No matter what, use this fetch:
http://ez.no/doc/ez_publish/technical_manual/3_8/reference/modules/content/fetch_functions/related_objects and this one to find the readers of a magazine.
You can use the related_objects fetch function ( http://ez.no/doc/ez_publish/technical_manual/3_8/reference/modules/content/fetch_functions/related_objects ). Set object_id to the id of your Lecteur object and attribute_identifier to the id of the lecteur/magazine class attribute.