I always have confusion in correct hand placement for decreased right rotation caused by left thoracic facet joint capsular tightness at T5-T6. What mobilization technique is used and what hand placement for extension, flexion and rotation of spinal levels?

The angle (or slope) of the spinous processes of the cervical vertebrae and those of the thoracic vertebrae differ considerably. The segment to stabilize and the segment to mobilize depends on what you want achieve i.e. opening/gapping or closing/approximation of the vertebral facets.

Will does a great job at explanation with his video ”biomechanics of the spine and spinal mobilizations’. I highly recommend it as it addresses all your questions.

Video