Wo muss ich das bayerische Ermäßigungsticket bestellen, wenn ich nicht in Bayern wohne?

You don’t have to have your residence in Bavaria. The place of training/work/studies also extends.

https://www.dbregiobus-bayern.de/tickets

You scroll down to the FAQs

then find that the first paragraph is relevant

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• Authorized users for the Bavarian discount ticket are
• Apprentices who visit vocational schools or comparable educational institutions in Bavaria OR have their main residence in Bavaria, unless you are entitled toFree of charge of schoolconsists of:
• Students with place of study in Bavaria, regardless of residence
• Students with headquarters in Bavaria who are studying semester tickets at a university with cross-border and valid in regions of Bavaria – this applies only to individual universities in the region of Ulm
• Voluntary service providers whose place of service or headquarters is located in Bavaria
• Officials:inside with office in Bavaria

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You fill out the form, let it be confirmed by the training company and can then use any of the providers listed at Bahnland.