The first step should always be to think about your personal objectives and circumstances with regard to the doctorate.
Most doctorates in the humanities and social sciences in Germany are individual doctorates.
There are no fixed deadlines or selection procedures for the individual doctorate. Instead, it’s about coming to an agreement with your supervisor on your topic and the exact conditions you must abide by (scope, time schedule, methods, details of supervision, possible funding) as well as clarifying the formal requirements for your doctorate and applying for acceptance as a doctoral student at the JGU.
In this case, the first step is to identify and contact a suitable supervisor at JGU and convince them of the potential of your doctoral project.
The various faculties and schools at the JGU are responsible for accepting their own doctoral candidates – in the case of Theology, the Catholic and Protestant faculties, and for students of music and art the Mainz School of Music and the Academy of Fine Arts. In addition to your supervisor, the dean's office or rector's office of your faculty or school can also advise you on all formal questions regarding acceptance as a doctoral candidate.
All further information can be found here: https://en.gshs.uni-mainz.de/doctoral-studies-administration/.