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I can obviously access the (pretty awful) SYD QF business lounge. By virtue of it being a Skywards booking/EK ticket number, can we access the Emirates lounge instead?
https://www.emirates.com/au/english/...rtners/qantas/
It mentions Asia but does not indicate Japan.
If the agreement includes Japan (as part of Asia) then being in Qantas Business class should be enough for you to access the Emirates lounges - if it is open.
QF25 currently departs about 9:30pm. The EK site shows the SYD lounge as being open
04:00 - 06:00 and 17:10 - 21:00, so on that basis you should be fine.