Soak wood chips in water to cover at least 30 minutes.
Combine 6 cups water, salt, and sugar in a bowl, stirring to dissolve. Rinse scallops, and stir into brine. Cover and chill 1 hour; drain.
Arrange scallops in a single layer on a wire rack; chill 1 hour.
Prepare charcoal fire in smoker; let burn 15 to 20 minutes. Drain chips, and place on coals. Place water pan in smoker; add water to fill line.
Wrap strips of prosciutto around scallops, securing with wooden picks. Place scallops on upper rack. Place rack in smoker. Sprinkle green onions over scallops (most will drop into water); cover with smoker lid. Cook 20 minutes or until done.