Knols books can be published in various ways.
A single author can write the full textbook and some of the chapters or sections can be coauthored by other authors.
Equity Research - Online Textbook on Knol was announced which will be developed on the basis of single author knol textbook. But initially, knols by other authors are being collected to present quickly study material to knol visitors in a book format.
A knol book can be developed as a collaborative textbook. In a collaborative Knol textbook, different authors write different chapters and this is predecided for authors join the collaboration as they come to know of the book's development.
Knol book of readings can also be developed. This model was started sometime early but was not used that frequently. Once again on Knol this model is becoming popular.