According to oneworld.com it is either the Royal Orchid or Silk Lounges.
http://www.oneworld.com/ffp/lounge-access
Note that you can also use any oneworld operated lounge as per oneworld rules.
And if so, considering that Thai is a star alliance member, does this even make sense?
There are plenty of examples (not just limited to QR) of an operator having a contract with a third party lounge whose operator is in another alliance.