Synthesized answer
The provided passages do not contain information about what questions remain unanswered in the book "Brief Explanation of the Laozi". The passages only offer a description of "The Classic of the Way and Virtue by Laozi" and its attribution to Lao Tzu [Passage 1].
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: The Classic of the Way and Virtue by Laozi Description: The most famous and influential Taoist text, the Tao-te Ching is traditionally attributed to Lao Tzu, supposedly a contemporary of Confucius (551-471 B.C). Categories: History Pages: 260 Snippet: The most famous and influential Taoist text, the Tao-te Ching is traditionally attributed to Lao Tzu, supposedly a contemporary of Confucius (551-471 B.C).