The book "Sy-Hugenotten" by Oqueka and Wendt [1981] can be found in the on-line catalogue of the Family History Library in Salt Lake City, which can lend a microfilm copy of the book to any Family History Center in the United States (maybe not in Germany because of privacy laws). Also, Hans Wendt once gave me a printed copy, so I can provide look-up and photocopies if you can be more specific about the inquiry.
Michael Schulz
Redwood City, CA 94061