There are two tables that the gift cards use for storing information:
wp_pimwick_gift_card
Stores the card number, expiration date, and active flag.
wp_pimwick_gift_card_activity
This table contains the transaction log to record loading and redeeming the card. Columns include activity date, action, amount, and note.
Note: it is assumed your site prefix is “wp_” (the default) however the table names may be slightly different depending on how your system is configured.