To search in your Order Management System (OMS) for all orders which used a specific coupon code, go to Orders / Advanced Search. Enter your order criteria if any, and enter the code in the ‘Coupon Code’ field. Click Search.
You can also determine coupon uses by navigating to the Coupons section of your OMS, then finding the coupon in question and clicking on the underlined hyperlink for the coupon code. You will see Coupon Uses at the bottom of the screen.