According to the resolution of the Conference of Health Ministers of 2014 (GMK 2014), foreign doctors must Professional language examination on C1 Level exist in order to be licensed in Germany. In the GMK's key issues paper, the Requirements described in concrete terms

87th Conference of Health Ministers (GMK 2014:3)

„Applicants must possess the German language skills required for comprehensive medical practice. They must be able to communicate the content to their patients without significant queries understand and in particular so spontaneous and so fluent to be able to understand that they can carefully take a patient history, inform patients and their relatives about findings and a diagnosed illness, present the various aspects of further progress and explain the advantages and disadvantages of a planned measure and alternative treatment options, without having to noticeably search for words more often. In collaboration with colleagues and professionals from other disciplines, they must clear and detailed to express that in patient presentations as well as medical orders and instructions Misunderstandings and based upon this Misdiagnoses, incorrect therapy decisions and Therapeutic errors are ruled out. Furthermore, they must also the German language to have a good command of written [language], ... in order to properly maintain medical records and issue medical certificates.“

These requirements should give you an initial indication of what you need to demonstrate in the specialised language examination. For targeted exam preparation, it is also helpful to know the exact definition of „C1 level“.