spctl "command not found" on Recovery start (mac OS Big Sierra)
You seem to have booted into an older version of macOS Recovery (there's an item called "Install OS X Yosemite.app" visible in your screenshot). This is something that can happen with Internet Recovery, depending on the Mac model and OS version.
If you use the regular local Recovery (⌘ R), the spctl command should be available.
If you HAVE to use Internet Recovery, try ⌥ ⌘ R. This should load the latest version of macOS compatible with your Mac.