forgot the name for the time being
recycles fumes. Think one tube goes to the Canister and the other to the inlet pipe?
Impact of not having the plug in - bugger all. unless your concerned about the environment.
You own a skyline so that's a no.
Normally one of the plastic pipes the tube goes onto breaks. Maybe someone removed the unit the plug connection plugs into in the centre back of the firewall on that brass bracket.
Where your knuckle is in the picture