As I said
as long as the suspects are within German borders the local law enforcement units and court have the authority and they are to be sued by the German laws except if they are in wanted list in Turkey and Turkey request extraditing of the suspects in order to be sued by the Turkish law. In this case Turkey have the authority over threats on Turkish territory and can only ask for support by the German authorities for the arrest and extradition. Turkey can act legally on German territory only by the request and the knowledge of the German authorities otherwise the situation is going "else where". If we have to be objective with the relations between Turkey and the EU and the special behavior that EUROPOL and other services of the member states of EU are showing to the PKK and the organizations with different names under the wing of PKK yes you can report to the local authorities but in the process of collection of evidence or in the court trial if there is any I am very skeptical of fruit giving work to be done. Its a little bit long but there is two part documentary of TRT World about PKK in Europe and its activities. It also delivers the EU service's point of view on the matter and actually ex- members of the security services that are sharing their experience with PKK. I will say it like in the documentary. Every year there is EU Terrorism and Trend Report coming from EUROPOL and every year PKK is listed there with its attacks in that report and they are not even listing their organized crime activities in the report. Maybe its in other report. There are some arrests but not enough and they are for the small fishes arrested on the scene while we have information of more high ranked and dangerous people walking around. Its clear that the problem is political and when there is political hand in something even the laws are not enough. I will post for you the two part documentary from TRT World and the EUROPOL EU Terrorism Situation and Trend Report. Even if you dont watch the documentary describing the actual behavior of the EU services on the matter I urge you to read the report from EUROPOL. If you do both then you will understand what I am talking about better.
https://www.europol.europa.eu/tesat/2017/index.html I recommend using of the PDF version.