Can you suggest a shoulder exercise I can do without further aggravating my scoliosis?

Safe. Scoliosis should not be aggravated by exercises to your shoulders. The only exception would be a rare condition, sprengel's deformity, where there is an issue with the scapula of the shoulder which gives an appearance like an upper thoracic scoliosis. This condition may be associated with restrictions in shoulder motion.
Go for it. I don't think exercise of any type would worsen scoliosis. To the contrary, exercise can provide further stability to the spine, which may help control symptoms sometimes associated with scoliosis.
Pilates, pool, gym. Before you begin an exercise program that focuses on your shoulders you should strengthen your core, including the postural muscles that support your spine. Pilates would be an excellent way to accomplish that. Then build your shoulder strength-aquatic programs or swimming would be a good start; add gym exercises such as shoulder shrugs, low rows, resistance bands. A trainer can help. Good luck!
Planks. Avoid overhead lifting cables work is easiest on shoulders are you talking about shoulder pain under scapula on the right side get massage control pain the.N strengthen careful begin with scapular stabilizers them shoulder work with pt you can't strengthen painful structures comfortably.