Is there a way to problematically get all schedules? I found out how to remove them using the web service but I didn't see a way to get them.
the nwadmin.exe offers a method called "EnumSchedules" which is supposed to display all workflow schedules of your farm.
See this article for further details on nwadmin tool: NWAdmin Operations - Nintex Workflow 2013
But I'm afraid it might work unproblematically