Assuming you are talking about USA I file a schedule c business income under my name as a sole propieter, otheres do it differntly, some parking companies send 1099's
that list years income others dont and I just add those to total income, I deduct reg fees and expenses ie: computer usage paper etc.
Sale of domains is a little trickier because it is still a gray area with IRS and not many court cases available, some list as capitol gains some a intellectual property such as a trademark sale, this last category is ok if this was your main business and the name was part of it according to irs, but for most sale of domains is treated like sale of inventory such as a store front.Best thing is get an accountant who knows domain names