Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
It's a good book to remind the main aspects of eneagram as a tool for self care, specially if you are familiar with the subject.
In the case you are having the first approach to eneagram using this book, the information is very limited from my stand point and I would look for additional books/information