The author's thesis itself is knowledge. Or, at the very least, it's an attempt at the transference of knowledge. This knowledge can then be absorbed by the reader. Until then, however, it remains no better than facts. Wisdom, even in the factual sense of understanding scientific formulas and relations, is what happens when the absorber begins to make connections in his head between bits of knowledge.
Wisdom is the understanding of knowledge, at least in the mental sense.
The next step, at least in FZ's hierarchy, is truth. Yeah, knowledge is murkier than information, wisdom is blurrier than knowledge, and truth is the grayest area yet. As the list of FZ's words moves on down the line, the concepts they are describing become less and less tangible, harder to understand and describe. Truth, then, is a step back. It's the process of digging one's head out of, well, his own head and taking a look around If wisdom is what happens when the reader can relate to knowledge in the mental and internal sense, then truth is what happens when the reader can relate to wisdom in the tangible, physical sense.