That’s a very interesting question and one that as of today is no clear answer to. However, in general black holes are made up of all sorts of mass as it absorbs all matter that comes close to its event horizon. One could also imagine that matter as we know it, composed of individual atoms with concrete protons, neutrons and electron numbers does not exist within a black hole. In fact, we do not know at all what the singularity within the black hole looks like, is made of or whether the physics we use and love today even exists. Nevertheless, even in “less” extreme environments such as neutron stars protons from hydrogen and helium atoms absorb electrons in a process called reverse beta decay, making the neutron star essentially a giant nucleus without protons and therefore eliminating any traces of the origin of these protons. So, to conclude although we do not know exactly what is within a black hole the pressure and heat are so extreme that it is easy to imagine that all matter gets degraded to its elementary make-up.