Creating a UX Certificate is a complex procedure. We will not only validate skills of one area but of multiple areas at the same time. You freely choose your focus for the certification. You know the field you want to work in mainly and therefore it is up to you to choose your best topic.
It is up to us, however, to certify you as a UX designer entirely. Therefore we need to ask you questions of many different fields to show that you have experience and knowledge in multiple areas and not only your most favourite one. That is due to the fact that being a UX Designer is a multidisciplinary job!