In Drupal 7, the RDF mapping for a bundle was attached to the entity on entity_load and could be accessed using $entity->rdf_mapping.
In Drupal 8, this property have been removed. The entity's mapping should be accessed using one of the following functions:
When loading a mapping to edit it.
When loading a mapping to place it in HTML.
For more information, see https://drupal.org/node/2028865.