Travelling on SK as *G you do have acces to the NW lounge. Normally you need an invitation which you either get at check-in or at the gate. If you have along lay-over you need to talk to the lounge dragon.

Do note though that the lounge is nothing special - and is only worth it becasue the alternatives in the concourse is so poor. I miss the days when you had access to the Clubhouse.