Well, in essence, very few people are - and hardly any will be descended from African Americans who were exploitative slave owners (in the sense that they owned other African Americans in law for the purpose of exploiting their labour for economic benefit). In 1830, for example, we have evidence of somewhere between about 3,000 and 4,000 black slave owners (compared with more than 220,000 white slave owners) according to that year's census returns. The vast, vast majority of those individuals were people - usually men - who owned still-enslaved family members, friends or other loved ones for reasons that were not economically exploitative (e.g., purchasing them from a white master but then legally being unable to free them). The population of the United States today descended from any kind of African American slave owner is likely to be very small indeed given the incredibly low base from which it is starting.

This subject came up recently in a critique I wrote of an article that appeared on Vice.com, but I've written on this subject in more detail here a few months ago. The idea of widespread ownership of black people by other black people within the institution of slavery is something of a popular myth, one with less than savoury origins, and it simply doesn't hold up to scrutiny.