Even on separate tickets, SQ will check your luggage through to SK, so no need to reclaim and recheck. Just proceed through transit security and passport control to get to the lounge. You will need to go through passoort control once again to get back to the gate for your Manchester flight.

SK check in opens around 5am, and you can check in for the day once the desks are open..

If you have 9 hours, I would recommend heading in to town rather than sit in the SAS Lounge There is a thread in the forum somewhere with lots of handy tips for that.