You don't have access. Alaska is not part of oneworld.
Similarly, Alaska elites get BA lounge access in LHR if flying LHR-SEA but not Alaska lounge access at SEA-XXX.
They want you to buy the Alaska Lounge membership.
But it makes no sense, because UA AA and DL all allow access on international itineraries because of their alliances.
It's one of the weaknesses of AS.