Declaración de combinación de SQL

Incluya la columna ProcPOAmdDel_ChallanQty en la tabla de origen, es decir, temp

MERGE PurProcessPOAmendmentDelivery AS pod
USING (SELECT ProcPOAmdDel_ProcessAmendmentId,
              rocPOAmdDel_SemiFinProdId,
              ProcPOAmdDel_ChallanQty
       FROM #TempTable ) AS temp
ON pod.ProcPOAmdDel_ProcessAmendmentId = temp.ProcPOAmdDel_ProcessAmendmentId AND 
pod.ProcPOAmdDel_SemiFinProdId=temp.ProcPOAmdDel_SemiFinProdId 
WHEN MATCHED THEN 
UPDATE SET pod.ProcPOAmdDel_ChallanQty = temp.ProcPOAmdDel_ChallanQty;