To find the ecommerce log for a transaction, go to Tools > Logs > eCommerce. The log can be searched by multiple parameters, including the customer's name, the amount charged, and the IP address from which the order was placed. If you have the transaction ID of the transaction that is being disputed, it will be simplest to use that to search the log.
The eCommerce log entry will look like the following. For transactions on coreCLEAR, both the transaction request and the gateway response will be logged. The most relevant part of the log entry for dispute purposes is the Address verification information, which is highlighted in the screenshot below.
To export an entry from the eCommerce log to save for evidence in a dispute, check the box next to the entry in the list of log entries, and then click "Export selected to CSV" from the Action menu. For convenience, check the count of selected records to make sure that only the log entries you want are selected or else a large amount of extra data may be downloaded.