Where is the option to disable iTerm2 confirm window on Log off?
In macOS, you can find the preferences for any app by choosing the app name in the menu bar, then selecting Preferences.
In this case, the preference being referred to is this one:
That Preference is an iTerm2 preference.
In iTerm2 go to Preferences, choose the General icon. There is a section on Closing this includes Confirm "Quit iTerm2 (⌘Q)" command