We are travelling from SYD-BKK-CNX. SYD-BKK is in F and BKK-CNX in in Y (no F seats on the award

)
2 questions:
a) Will we even get access to the spa?
b) What services are we entitled to?
The Spa lounge is an international departure lounge and you are departing domestically.
You can show your F arrival, along with your Y domestic, BP at the domestic lounge and see if they're willing to let you in.