does anyone know if studies are held in English or German? on the web site it is given that studies are held English or/and German. is knowledge of German required?

For what program? If you're talking about the LLM in European and International Law from the Europa Institut, most of the curriculum would be available in English (with optional components in German), and German is not an explicit requirement for admission.

The exception as far as I am aware is if you were to pursue the specialization in IT Law, which is for the time being only available in German.