My name is Diego and I am willing to take the Extreme Networks Data Center VDX - Exam. However, I couldn't find an official guide/material to study, I was wondering if is there an official guide/blueprint for this certification?
There are no downloadable materials publicly available. Extreme trainings are not like vendor-agnostic or some other vendor classes where you prepare to your exam the way you like according to some list. Most probably you have to take part in the course before you can take an exam for the first time. Maybe somebody from training dept. is here so can assist you with your case.
Perhaps for the future some eLearning for all classes could be developed, or just some list of exam objectives so you would know what to focus on with your preparations based on docs and hands-on efforts.