Making its way around the internet is the question, “If you could get everybody to read one book, which would it be?” That’s an interesting question, but there are a lot of unspecified variables that will drive philosophers nuts. For example:
Should we assume that the book is available in all languages and formats? Or that everyone finishes the book? Or that they’ve read other specific works that help contextualize the book? Or that they’re sufficiently aware of or concerned with the subject to get something out of it? And so on.
So instead, let’s do something different and ask the following:
If you could pick one book for one person to read, which book would it be, and whom would you have read it?
For example, one could say:
Donald Trump: On Bullshit by Harry Frankfurt.
I’m not sure that would be a particularly good recommendation, as it is unclear whether Donald Trump reads, but you get the idea.
Let’s leave open to whom you can recommend the book, but note that your answer will make more sense to others the better known the person is. As for the kind of book, let’s leave that wide open, too. No reason to restrict your answers to philosophers or philosophy.