Hello Florian,
thanks for your reply. This resolved the problem.
A good guide how to enable the scheduler would be very helpful, but in the guide from help.sap.com wich is linked in my post, I can't find the prerequisite to have this role. Only the roles "sap.hana.xs.admin.roles::JobAdministrator" and "sap.hana.xs.admin.roles::HTTPDestAdministrator" are needed.
Regards
Andreas