In which table/column Pending Supplier acknowledgement flag is captured ?

Summary: When we enable the feature "Allow Delivery on Purchase Orders that Are Pending Supplier Acknowledgment" , the document status will always be Open irrespective whether PO is pending acknowledgment or not. But we can see in the Information icon that PO is pending acknowledgment. So my query is in which table this information is stored in back end. I am not asking for ACCEPTANCE_REQUIRED_FLAG as this will always be set at Y based on PO header irrespective if the PO is accepted or rejected by Supplier.

Content (required): We are building custom report and Pending acknowledgment field is one of the criteria.