This is the best list I've seen in this genre, because it excludes a lot of commands that you don't need and probably won't want to use in a modern mostly-GUI workflow, and even gives the appropriate scary warning for rm.

If you need something like dd, or any of the "real programming" stuff like if statements and xargs, you probably really love it all and will find it yourself. If you just do a few things in shell and use Python and GUI for the rest, these Are the main ones.

Slightly less common ones I'd add:

kill and killall

ps -aux | grep APPNAME

(Technically not a single command, but it's 90% of my use of ps or grep, so it might as well be it's own command)

cowsay, fortune, neofetch, and lolcat, sl

Not actually included in shell but people should know about them anyway.

It's said that Arch users are legally required to stare at the output of neofetch once per hour at minimum.

Various systemctl commands:

start, stop, status, enable, disable, mask

systemd-analyze critical-chain

nmtui (Not sure which distros include this by default and which don't)

dmesg

journalctl, dmesg

sudo reboot now

sudo shutdown now

units (Usually not included, gotta install it)

ping, ip a

Also, this would be fantastic to include in educational material or even add directly to a distro. Does it have a license?