The detailed sales report has a column called Price that can be compared to the Sold Price to determine the amount of discount, but since the report uses the HQ Item table to supply that field, it doesn't necessarily reflect the list price at the store, which may be different from HQ.
I like to use the TransactionEntry.FullPrice field, then calculate the difference to find discount:
You can memorize the Detailed Sales Report, and then open in notepad to add these columns:
Begin Column
FieldName = "TransactionEntry.FullPrice"
DrillDownFieldName = ""
DrillDownReportName = ""
StoreIDFieldName = ""
Title = "Full Price"
VBDataType = vbCurrency
Formula = ""
ColHidden = False
ColNotDisplayable = False
FilterDisabled = False
ColWidth = 1100
GroupMethod = groupmethodNone
ColFormat = ""
End Column
Begin Column
FieldName = "ItemDiscount"
DrillDownFieldName = ""
DrillDownReportName = ""
StoreIDFieldName = ""
Title = "Discount"
VBDataType = vbCurrency
Formula = "(TransactionEntry.FullPrice-TransactionEntry.Price)*TransactionEntry.Quantity"
ColHidden = False
ColNotDisplayable = False
FilterDisabled = False
ColWidth = 1100
GroupMethod = groupmethodSum
ColFormat = ""
End Column