how do you join cement board from a shower wall to drywall?
Other than being nailed to the same stud, it is not all that necessary that they be joined together. Just figure on the tile overlapping the drywall about a half an inch to kill the crack. You can mesh tape them together however and skim them flat with each other as long as you don't skim wide into the tile board area. You could do as little as just caulk the crack with silicone too.
