This is how to get the amount of remaining ink as reported by your Epson printer.

# For KDE:
$ kdialog --title "Ink levels" --msgbox "$(LANG=C escputil -qir /dev/usb/lp0 2>&1 | \
  sed -re 's/.*remaining.*/Percent of ink remaining/;s/([0-9]+)$/\1%/')"

# For Gnome:
$ zenity --info --title "Ink Levels" --text "$(LANG=C escputil -qir /dev/usb/lp0 2>&1 | \
  sed -re 's/.*remaining.*/Percent of ink remaining/;s/([0-9]+)$/\1%/')"

It may differ a bit if you’re using a newer/older Epson Printer. The above has been tested on an Epson Stylus C84 connected via USB.