By default, ENS is enabled in Calendar Server. For Calendar Server you do not need to do anything else to use ENS.
A user who wants to subscribe to notifications other than the alarms generated by Calendar Server needs to write a subscriber.
Sample ENS C publisher and subscriber code is bundled with Calendar Server. (See ENS Sample Code for Calendar Server.) Once Calendar Server is installed, the code can be found in the following directory:
/opt/SUNWics5/cal/csapi/samples/ens