Agents for Workitem for JV Park Workflow

Hi,

We are developing a report which shows the agent who has approved work item at different levels. For this we have to read the work items based on the posted document number. I tried the FM SAP_WAPI_WORKITEMS_TO_OBJECT but it is not returning any value. Is there any way that we can retrieve the Workitem id's involved in the workflow of posting a parked document?

Thanks,

Manideep Settipalli