Where to connect c wire at furnace for Honeywell Wi-FI thermostat
First off, the green wire should connect to the G terminal on the thermostat. It's connected to the G terminal in the furnace, and so should also go to the G terminal on the thermostat.

At the thermostat, the extra blue wire should connect to the C terminal.  Depending on the furnace (read the documentation, and analyze the schematic to be sure), you should be able to connect the other end of the blue wire to either of the C terminals in the furnace.