Er, everywhere - I have never ever been refused access to the lounge which the OneWorld rules say that I am entitled to as a OW Emerald, which is any OW lounge at that airport.

I've been in ACs in many US airports, the AC at NRT, the FLs at ORD, LAX, LHR. Pretty much all of CX's lounges worldwide. BA/QF lounges at LHR, LGW, SOU, JFK, SFO, LAX, BRU, SYD, SIN, MEL, and others. AY at HEL. EI at LHR, DUB... [This is by no means a complete list]

Obviously this is only when flying on a OneWorld marketed and operated flight that day from that airport (except for CX J lounges which I can access any time).