Gray Hat Hacking: The Ethical Hacker's Handbook is excellent and covers a lot of topics. Depending on your technical knowledge, I'd also recommend something like Nmap Network Exploration and Security Auditing, and something like Kali Linux Hacking: A Complete Step by Step Guide to Learn the Fundamentals of Cyber Security, Hacking, and Penetration Testing, and/or a Python for Penetration Testing book. Learning the tools teaches concepts you can use everywhere. More on reddit.com

https://www.pdfdrive.com/search?q=pentesting&pagecount=&pubyear=&searchin= Buddy of mine recently told me about this page. More on reddit.com

Kinda just anything you are interested in. I mean, that sounds super cliche' but the reality is, it's a broad field. There's endpoint security, network security. Pentesting, compliance. There's just so much to explore. My 2cents though, start with some history. Be able to speak the lingo and live the war stories out with potential peers who've been in it for a long period of time. Asking a coworker about eternal blue  or what did they think when stuxnet was circulating the news are huge ways to begin connecting with individuals in the field. Personally, I love Sandworm and Tracers in the dark for this reason. But there are other books you can read like from 'hacker legend Kevin Mitnick.' To get a little sense on how hackers kinda stumbled into the scene through phone phreaking. I'll end there. If you want technical resources start by figuring your niche first. If you want broad security concepts read some comptia books. More on reddit.com

The easy and broad answer is Security Engineering by Ross Anderson. Whoever works in CS gains something from reading this book. More on reddit.com