You'll have to combine SQ and VA flights - SQ from BKK via SIN to one of the Australian east coast cities it services, then VA domestic to Hobart.
You'll need to research reward seat availability with both airlines and the cost, then work out the best way to book.
You can't book multiple airlines on the SQ website (that would require a phone call) but you might be able to get the whole itinerary to show on the VA website by searching for BKK-HBA one-way.
Keep in mind you can't transfer KF miles between members, but you can Velocity Points.
You can transfer from VA to KF and vice-versa at a 1.55:1 exchange rate.
Good luck!