Mod key is Super, known as the 'windows' key. If you're using @rockedge's iso MOD+z brings up a splash screen with keybindings. which I made, but checked against the iso, and I don't think they are all incorporated, but many will work.
If you look at the file /root/.spectrwm.conf, the bottom of the file will have any added keybindings, and there's a section above that defines some keys to certain applications. Seen at the lines below click to enlarge:
EDIT: I noted the missing keybindings here: viewtopic.php?p=101452#p101452
ALSO: use MOD+d to open the Rofi application menu to launch programs
and this contains a section with default keyiindings, many which have been changed, but many left in. As a rule if they have not been redefined in spectrwm, then the defaults are still present. I'm working on getting us on the same page with the keybinding situation:
https://github.com/conformal/spectrwm#readme