My fave: Every single Hal Pomeranz webcast. Seriously. There is no better answer than this. Why? Because Hal tells us how to understand it and why it’s that way.
Kali Linux Revealed is a fantastic introduction to Debian and Linux, single system admin, package and service mgmt, image building, and what's special about Kali, free online at kali.training from Off-Sec or in print. Then one might enjoy Hal's Linux Forensics course !
Hal,
I have always been partial to the Unix and Linux Administration Handbook. I think I have the first four additions, But then again, I am an old fart. ;)
Was my getaway drug: kofler.info/buecher/linux/
We call it as "The Kofler" since it was more or less the single comprehensive book in german for years.