You can easily find the PIN for all your cards in the application. Go to "Finances" section at the bottom of the main screen and click on a card. The option "Show PIN" will be visible. First you need to enter the passcode that you use to login in the app, then the PIN for your card will appear for 30 seconds. 

For security reasons, this option is only available on the mobile application; you cannot consult your pin code on the computer.
The PIN code will not be displayed if you do not have a plastic card. Check the article: How to order a physical card and when will it be delivered?