Your CAN is located on the front of your ID card - on the top right of the German National ID Card and eID Card, and on the bottom right of the electronic residence permit (“elektronischer Aufenthaltstitel/eAT”). You will need to enter it if, for example, you have entered your personal six-digit PIN incorrectly twice.
You can find more information here: Registration & identification with the eID function of your ID document.
If you have any questions, please contact us at support@kulturpass.de.