I was recently asked by a colleague to help him find all the Listener ports that were being used in the Enterprise .
While Grid Control Doesn't provide a default report for this . All the data is available in the Grid Control repository. A Simple Table Based report based on the below query can be used to get that data
SELECT mgmt$target.host_name,mgmt$target.target_name,mgmt$target.target_type,mgmt$target_properties.property_name,mgmt$target_properties.property_value FROM mgmt$target, mgmt$target_properties WHERE (mgmt$target.target_name = mgmt$target_properties.target_name) AND (mgmt$target.target_type = mgmt$target_properties.target_type) and (mgmt$target.target_type='oracle_listener') and (mgmt$target_properties.property_name='Port');
The Above SQL Will Display all Listener's and their ports.
the MGMT$target and mgmt$target_properties can provide and great deal of other options and reports based on Block Sizes and other parameters set can be used to quickly find issues in your enterprise.
P.S The above query is based on the Grid Control 10.2.0.5 Repository