Accordding to Qantas's policy listed at https://www.qantas.com/agencyconnect...hrough-checked , if it is QF to QF/EK , then baggage can be checled through. Whether in the specific situation queried, it depends on whether Sydney Airport allows the bags to be checked through given there being an overnight stay
The poster hasn't indicated what airline is operating the Sydney to Bangkok sector , but given that the only airlines that seem to offer service on that route are QF, TG and XJ, it seems that QF would be the only option for a QF award booking