Why would you want to update certificate type questions?
It is possible that there is a third party solution where supplier certificates already exist and we just want to replicate this data to SAP Ariba. Instead of the supplier specifying the data one more time, the data can just be synced from the existing "repository".
So, how do I update certificate questions in a supplier questionnaire?
To have an idea of the body structure required by the API for a certificate type question, I used Chromium Developer tools and captured the request sent when updating the question. Within the request I extracted the item that belongs to the certificate type question and used that as a starting point.