Hi Arun
Please use FM SAP_WAPI_WORKITEMS_TO_OBJECT to get all the associated workitems for an object.
You will have to pass the Quality Notification Object and a Key to it to get all workitems. Then maybe you want to filter based on status or date and so on....that depends on your requirements.
A similar kind of requirement was there in the following thread (the BO will be different for you)
http://scn.sap.com/thread/3561190
Alternatively, you can query table SWW_WI2OBJ to get the workitem IDs and then use SWWWIHEAD
Regards,
Modak