Several of Martin Grabmann’s works are available in digitized form via the Internet Archive including the English translation of his classic Thomas Aquinas: His Personality and Thought.
Here are the German texts that are available through the Internet Archive:
Die philosophische und theologische Erkenntnislehre des Kardinals Matthaeus von Aquasparta: ein Beitrag zur Geschichte des Verhältnisses zwischen Augustinismus und Aristotelismus im mittelalterlichen Denken
Unfortunately only the first volume of Grabmann’s history of the scholastic method is available. This volume covers the patristic period to the beginning of the 12th century. I cannot locate a digitized version of the second volume online, which covers the 12th century to the beginning of the 13th. Perhaps one of our readers could help us out here.
If you are looking for Thomas von Aquin, Personlichkeit und Gedankenwelt, the original German text of Thomas Aquinas: His Personality and Thought, you will not find it at the Internet Archive. You will not find it on Google Books either. But it is available here at the Hathi Trust Digital Library. While you can read and search the text online, you cannot download a PDF of the complete version unless you belong to a college or university that is a partner of the Hathi Trust Digital Library.