You will be domestic.
Once you have been flying for a certain period of time (12m) you are eligible to apply for a casual position with Team Jetstar and if you are successful you will be in the position to be 787 trained.
Not all TJs get 787 training. When you have it, it might be only on the random Occassion you would get a trip. Usually once a year for expiry purposes.
There isn't much ability to transfer over to JQ international as the majority of the crew is Foreign.
You will, however still get to do international flying on a narrow body- the narrow body international flying is mostly ex MEL and Syd and mainly grabs Tasman, Fiji and trips to SIN and DPS via PER.
They like sending the casual crew on these because they are flexible with what they can use you for and You don't get paid overnight allowances.