The all commands section is the first entry in the drop down menu at the bottom left. To access all commands you can either select it from the menu or use the hotkey:
ctrl + 1 (Linux/Windows) / cmd + 1 (Mac)
The all commands section shows you all commands from all menus and sub menus. This includes Nuke’s standard commands and also custom commands from custom menus and sub menus. This section is the entry point to having all commands at your finger tips and creating new collections.