[in German]: c’t article with detailled template letter to enact data subject access rights [c’t is a popular German IT magazine] – They call it the “torture questionnaire”…
(link at the bottom of article)
https://www.heise.de/ct/ausgabe/2018-5-Die-DSGVO-bringt-den-Buergern-neue-Rechte-3965940.html