The Product Code will be provided after you have finished the payment process. It represents your individual license for the software. (Described in the email at the time of purchase.)
Check your inbox for an email with the subject line "Korg Shop:Product Code". If you cannot find such an email, please access to your account page in korg.shop , then select an order. You will see the code at the item section.
You will also be asked to provide the Product Code in order to obtain support, so please do not discard it and keep it in a safe place. (Please note that KORG cannot re-issue a Product Code.)