How do i show discount per product?

Thanks for posting in the Community, basicinfo.

I'll help you add a discount per product as a line item on your invoices or sales receipt. 

1. Click on the Gear icon and select Products and Services.
2. Select New.
3. Select Non-inventory or Service for the type.
4. Name the item Discount. If you want to create multiple discount items, give them unique names so they're easy to tell apart.
5. In the Sales price/rate field, enter the discount as a negative amount. Keep in mind, this is an amount and not a percentage.
6. From the Income account drop-down menu, select the Discount given account. QuickBooks creates this account for you when you turn on the discount feature.
7. Select Save and close.

Once done, you can select this item on an invoice if you would like to apply a discount on a certain product.

As of the moment, we don't have an option yet to apply a specific discount amount or percentage on the Products and Services list. It's best to share your request directly with our product developers by sending feedback. To send a feedback, go to Gear icon and select Feedback. 

Lastly, you can check on this article for your reference: Add a discount to an invoice or sales receipt in QuickBooks Online.

Keep me posted if you have other questions or concerns about using QuickBooks Online.