You can use the XML-API to accomplish this. The documentation for the XML-API can be found at
http://www.cpanel.net/plugins/xmlapi/
There are also numerous threads discussing the usage of this API that you might find beneficial.
Examples of the requested functions:
List add-on domains for an account:
Code:
https://${SERVER_IP}:2087/xml-api/cpanel?user=${CPANEL_USER}&xmlin=<cpanelaction><module>Park</module><apiversion>2</apiversion><func>listaddondomains</func></cpanelaction>
List parked domains for an account:
Code:
https://${SERVER_IP}:2087/xml-api/cpanel?user=${CPANEL_USER}&xmlin=<cpanelaction><module>Park</module><apiversion>2</apiversion><func>listparkeddomains</func></cpanelaction>