Refined #: a missing buccal wall of the bone caused by extraction trauma is best rebuilt by what dental specialist? I hope you can all agree.

Oral surgeon . Either an oral surgeon or periodontist.
Any dentist DDS/DMD . A missing buccal wall is so easy to repair, any dentist with enough education and experience in this area can get the job done and get a great result. It's all in the wrist, so to say... Success or failure depends mostly on the materials used, the health of the patient and whether or not the patient follows instructions after the procedure is completed.
Skill, not degree. I think we would all agree that the best dentist to rebuild buccal bone would be the most qualified dentist that you can go to. Typically a periodontist or an oral surgeon would be the two specialists trained to perform such treatment. Honestly, it's not the degree but the experience, training and skill of the individual dentist that makes the most difference. Everything being equal, periodontist.