What are the different API available to retrieve Process Reporting specific detail?
You can find a lot of the information on the AtomSphere APIs here: AtomSphere API
I think you are specifically looking for:
Execution SummaryRecord object
The first link will show you how to retrieve Execution Record objects which contains information about a process execution.
The second link will show you how to retrieve Execution Summary Record objects which summarizes the executions in a block of time (including processes running in Low Latency).
Retrieving data ...