Are you talking about two cards saved on your PayPal account? If you have two, one of them will be listed as the primary card, you can check which one is primary just by going to your "account" and check your payment settings. If your primary card doesn't have enough to cover the charge, the secondary card will be used instead, but PayPal will send you an e-mail if this happens.
Regardless, you should have gotten a receipt e-mail from paypal that lists the last 4 digits of the card used, your you can log into PayPal, click on "recent transactions", find your payment and click on "details"
