If I wanted to work my left external oblique and quadratus lumborum, while contralaterally working my right internal oblique would I hold the weight in my right hand and bend down to the right side? then pull myself back up using my left?
To work the left obliques, hold the weight in your right hand, bend down to the right, and straighten back up.
To work the right obliques, do the opposite.
Honestly, just go do some side bends and you will know which side is working, it’s not rocket science.