Welcome to Flyer Talk justme147433

If your bags are tagged through to Brisbane by Frontier (baggage tag will show DEN LAX and BNE if this is the case) then you will not need to touch them at LAX. Otherwise you will need to collect them at T6 and carry to T4 to check them in with Qantas.

T4 is not too far from T6. I'd take the escalator up to the upper level to walk along under cover in less enclosed space (noisy, traffic fumes). Turn left out of T6 and it is a few hundred yards along. If you reach the end of the U (at TBIT terminal) you have gone too far.

You will need to check in - Qantas counters are at the far end of T4 (closest to TBIT), deposit checked bags if they weren't through tagged, and clear security upstairs. If you are flying in business class, or have oneworld emerald or sapphire status you can use the priority security lane (entrance closest to Qantas check in), otherwise it is the main lines. If you are flying in business class or have oneworld emerald or sapphire status then you can use the joint Admirals Club / Qantas Club lounge (or Flagship Lounge if oneworld emerald) on the right hand side of the pier to await your flight.