The use case here is to get the information of content with type cq:Page and dam:Asset that is being installed/updated in the JCR using package manager in AEM.
I would like to know if there are any event listener or API's that can be used for this purpose.
AEM 6.2 is being used here.
Pages are just nodes. You can write an event handler that uses the javax.jcr.observation.EventListener.
Hope this helps...
The same can be done using workflow launchers as well which would trigger on creation/modification of node types 'cq:Page' and 'dam:Asset'.
Have a custom process step that generates a report consolidating the information about the workflow payloads in action.