The hotkeys are defined and can be customized in Zero-K/LuaUI/Configs/zk_keys.lua
You can find the defaults
here. I don't think that these are all hotkeys though, and it certainly doesn't include all the modifier keys you can use. Just look at
all the modifiers you can use for guard...For now I think the best way to learn them is to read through the wiki. It would definitely be cool if somebody could make an easy to read cheat sheet though.