I suspect the book that would improve the software engineering world most if all software engineers read it and really took it in would be "Everyday Sexism" by Laura Bates. Understanding how shockingly sexist the world is in all kinds of different ways, and then thinking how that applies within the software industry, might help us to overcome it - both in terms of our own industry diversity, and building products which better serve all users. (There are plenty of other great feminist books of course; that's just one that I know is pretty accessible and has the kind of data/evidence that I suspect a lot of existing software engineers may find compelling.)
That's a serious answer, but if you really pressed me for a programming book, I'm not sure what I'd recommend, other than C# in Depth of course. I have shelves and shelves of programming books, and I rarely use them. I do think books are a great way of learning a language or framework, mostly because they're structured knowledge, designed for the task - all the information is usually out there already, but you don't know the order in which to read it. Books provide that ordering, as well as a consistent narrative and approach - hopefully, anyway.