There is Codarts in Rotterdam, which is a good school in my opinion, if you want to add movement/expression to your diabolo. Arjan and Dixie are teaching some hours a week. The main juggling teacher, also for diabolo players, is Gregor Kick. He comes from club/ball juggling, not diabolo. He is good in making your training structured, your posture clean, and aware about your artistic choices.
As said above, there are different schools, with different style. School A may be good for one person, and bad for another one. To know more about a school you are interested in, I would recommend contacting the school and asking if you can visit it. In some school you can even follow the program for a week.
From what I know, there is no higher education in Circus in Europe that are super good for pushing your diabolo technique. Taiwan and Malaysia might be good for that. The schools in Europe are good to improve your technique a bit, while improving your performance skills, physicall skills (accrobatics...) and finding your concept and style.