You can get to this part of the system by clicking on Reports in the blue Admin Toolbar and then clicking on the report you want from the menu.
Coupon Usage Report
You can view all Coupons used in whatever time-frame you need in this useful marketing report. Coupons you create (from Products > Coupons) are listed by Coupon Title in descending order with the highest Quantity Redeemed at the top and the Discount Total for each. The report also shows the total number of unique coupons used during the period and the Total Discounts for the period. You can use this report to see how much your marketing efforts through Coupons are costing you so you can plan your future marketing through coupons. Please note, this report does not track Reward Coupons redeemed; it tracks coupons you manually create in Products > Coupons and for most clients, this will be for web use, primarily.