What should an advanced user know? Everything provided by coreutils, stuff that goes in /bin etc? Also sed, awk and common tools for simple text processing?
However, I will say that learning how to effectively use grep and sed are probably the only big omissions from my list. But, those are outside the scope of this little book given those commands have whole books devoted to them.
Knowing a little bit about writing valid ksh/bash shell scripts (being at least aware of bash-isms) would certainly be useful for sys adm work.
My opinion is that the full gnu (and/or bsd) userland has grown so large over the years, that saying that you should know it all is probably overkill -- but knowing how to look things up (man, info) is a must.
As Zed's implied -- GNU documentation could stand to be improved vs bsd man pages -- although the info manuals can be quite useful.
In general I found these 14 commands end up being the smallest number anyone really needs to do basic CLI work, but keep in mind that the goal of the book is to give someone just enough experience to be able to go through my other books. There are plenty of more in-depth books on managing a server, so I don't bother to duplicate their work.
If you really want to learn how to manage servers and work the CLI, then check out "UNIX and Linux System Administration Handbook (4th Edition)" by Evi Nemeth and friends. My recommendation to people is to get a crappy computer you don't want, put OpenBSD on it following their http://www.openbsd.org/faq/faq4.html guide exactly, use the Nemeth book to configure every service you can and then point a security scanner at your box (like Nessus, or whatever they use today).
Once you can setup an OpenBSD box, get services running on them, and secure those services based on known attacks, then you can pretty much do anything. More importantly, OpenBSD is very bare bones so you learn the core of how a Unix system works and how to configure it, but their docs are very thorough and complete so you can do it if you follow them accurately.
Hope that all helps.