Depending on the option selected in the Accounts configuration page, the discount is either applied to the Unit Price (i.e before the line total is calculated) or on the pre-tax amount (after the line total is calculated).
In a Document Line Item table row using a Discount Item
This method uses a Discount Item to represent the Discount. To use this add the Discount Item onto the Line Item Table directly beneath the row you want to apply the discount to.
The Item applies the Discount percentage (or fixed amount) to the net amount (pre-tax) of the preceding Item’s unit price.
The discount is posted to the General Ledger. Set the account the Discount Item posts to on its Accounting tab.
Display Discount % and the respective amount on screen, when printed.
There are two columns to display discount ‘Discount’ and ‘Total Discount’. These can be configured on the Document Template to display % and amount respectively.
Go to Sales Order>Configure>Sales Order Templates> and choose the template.
Check which column(s) and in what mode you want them to be displayed i.e. ‘...when printed’ and ‘...appear on screen’.