Every now and then some amazing book comes out. And then comes people who insist that "you're not a real developer" unless you've read that book. I was reminded of this while reading reviews on Amazon for some of the hot books out there. While there are core competencies that every dev should know, there are also a lot of fringe topics, and multiple books on the same topic. And while a lot of these things are valuable, I think such an exclusive approach is damaging because it emphasizes not what you know and can apply ("can you write code with design patterns"), but rather what you've read.
For example, of course the GoF design patterns book is phenomenal. However, is it really that bad if someone read the C# translation of it instead (Design Patterns in C# by Steven John Metsker), or even skipped the books and went with purely online tutorials? I'd expect a "senior developer" to know what a design pattern is, recognize the buzzwords, and know how to apply them. However, if they got to that point from a different path then "normal" (?), I think that's okay. Part of the problem is that one cannot read it all, so it effectively encourages bluffing - developers buy classic books and display them on their bookshelf like trophies, and are afraid to let on about their shortcomings for fear of being rejected.
In short, I think it's far more effective to offer positive criteria like "developers on this team must be fluent in design patterns, automated testing, and writing clean code", as opposed to exclusive criteria like "you must have read book X".