Obviously a very reductive question -- even if sharpened slightly to "most influential" book. I will reduce it even further: one of the few books that I have read twice (and the only one that has exerted different, profound influence on me on each read) is Tracy Kidder's "Soul of a New Machine." This is a book that every engineer should absolutely read, though not without an uncritical eye for Tom West and Data General. I wrote about my second read of "Soul" five years ago[0], and I know that there are folks who have read it on my recommendation -- and I don't think anyone has regretted it.

[0] https://bcantrill.dtrace.org/2019/02/10/reflecting-on-the-so...