The end of discovery
The book surveys various areas of science - mostly physics - and for each one finds questions which we don't know the answer to. The book starts with a look at consciousness and the brain, and moves on to the big bang, the anthropic principle, extraterrestrial life and the nature of space and time. The second half of the book is about particle physics and quantum theory.
But the book doesn't 'do what it says on the tin'. It isn't an exploration of the limits of knowledge. Rather the questions posed are likely to lead to new areas of discovery. Certainly something like the discovery of extraterrestrial life wouldn't be an end, but a beginning. OK, so there are some questions which are more metaphysical than scientific, but even those can catalyse the development of new scientific ideas. I think the book might be useful as a gentle introduction to some difficult scientific topics, but those with more knowledge of the topics looking for thought provoking ideas may well be disappointed.