Hi Jitendra
You can use the CHECK Method , use the parameter 'IM_HEADER' whose Type is IF_PURCHASE_REQUISITION.
The interface IF_PURCHASE_REQUISITION has a method called 'GET_ITEMS', Method get_items will return all the items of PR. ( IF_PURCHASE_REQUISITION_ITEM->get_item will return every single item)
Regards.
Qingda Niu