The chargeback notification email which was received contains the receipt link, which is a link directly to the transaction in question:
If you are logged into the Toast Portal (a.k.a. "the back end"), this link will bring up a receipt to the check in question directly.
Using the Find Checks Tool
The check in question can also be found via the chargeback notification itself. The "Draft/Ticket #:" field contains the information which can be used to find the check in question.
With this information, navigate to the Find Checks tool in the Toast Portal:
From within this tool, navigate to the "Find by ID" tab and enter the draft number in the "Payment Reference" field and click "Search." This will pull up the check in question.
A link to the receipt can also be found here, via the "Actions" drop-down list: