/usr/share/nautilus-scripts/ShowDebugOutput is in nautilus-script-debug 0.9.2-0ubuntu3.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | #!/bin/bash
zenity --list \
	--title="Nautilus Scripts Environment Variables" \
	--width=800 --height=600 \
	--column="Name" --column="Value" \
	"NAUTILUS_SCRIPT_SELECTED_FILE_PATHS" "$NAUTILUS_SCRIPT_SELECTED_FILE_PATHS" \
	"NAUTILUS_SCRIPT_SELECTED_URIS" "$NAUTILUS_SCRIPT_SELECTED_URIS" \
	"NAUTILUS_SCRIPT_CURRENT_URI" "$NAUTILUS_SCRIPT_CURRENT_URI" \
	"NAUTILUS_SCRIPT_WINDOW_GEOMETRY" "$NAUTILUS_SCRIPT_WINDOW_GEOMETRY" \
	"pwd" "`pwd`" \
	"\$\$" "$$" \
	"\$0" "$0" \
	"\$1" "$1" \
	"\$_" "$_" \
	"\$#" "$#" \
	"\$*" "$*"
zenity --list \
	--title="Nautilus Scripts \$@ Variable" \
	--width=600 --height=400 \
	--column="\$@" \
	"$@"
 |