What kind of doctor sees somebody for altitude illness?

Travel Medicine: Altitude illness is caused by the body's poor adaptation to sudden increases in altitude. Your travel medcine specialist can help you learn about it, review your travel plans (rate of ascent) and provide protective medication. If you are suffering from altitude illness the only reliable treatment is to descend. Usually emergency or wilderness doctors treat this.

Travel Medicine: You did not specify in your question if you already have symptoms or are trying to prevent getting symptoms. Assuming that you are not ill now, i fully agree with dr. Kohl's answer. Please see a travel medicine trained physician in your area.