看到我co-supervisor给我的学习计划签名下的职称是Ph.D. (Privatdozent), Group Leader

Privatdozenten 编外讲师，私人教师

自己找到了。。。。。。
Private docent (abbreviates P.D. or Priv.-Doz.) is a title conferred in some European university systems, especially in German-speaking countries, for someone who pursues an academic career and holds all formal qualifications (doctorate and habilitation) to become a tenured university professor.

Becoming Privatedocentship is conferred to academics who have earned a doctorate (promotion) and then have written another thesis for habilitation and given a lecture before the respective department or faculty of a university. If they pass the vote after that lecture, they receive the venia legendi (or, rarely, venia docendi) and thus the status of P.D., roughly equivalent to the status of an associate professorship，