You'll get your receipt two ways. First, via email to the email address, you provided at enrollment. Second, there will be a copy hosted under Transaction History in the Savings section of the GasBuddy app.
Note that the pump does not show the discounted price. Instead, the discount is applied directly to your checking account.
You will see the discount details on your e-mailed receipt from GasBuddy, as well as in the Savings section.