+ The foundation of computer science is Knuth's The Art of Computer Programming . Everything else is footnotes. Knuth is hard. And easy. And everything in between. You won't understand all of it. But you'll have to be ok with not understanding all of CS anyway. Nobody does. You can spend your time searching for a silver bullet. Or you can just read the manual. Knuth is the manual. + Bach's The Design of the Unix Oper…
Unpopular opinion: I have _never_ had any real use of TAoCP. I own all volumes and have really tried to make use of them but they feel more like a trivia book than something you can actually use in your work. Sure, it's cool to own and recommend it but have people actually used it? To end on a more positive note: I highly recommend "Introduction to Algorithms" by Cormen et al. Not as cool but very useful.
Per the question, the context of my answer is learning CS and in particular self-directed learning. If the question was about resources for work, I'd probably say "StackOverflow" and be done with it.