Cobalt ferrite nanoparticles have been attracting considerable interest in the recent years because of the large number of potential applications, including magnetic storage, magnetic fluid hyperthermia and as contrast agents for magnetic resonance imaging. Physical properties of this class of materials depend critically on a number of parameters, including crystallinity, stoichiometry and cation distribution. In this work we have performed a Resonant Inelastic soft X-ray Scattering (RIXS) study on a series of 5 nm cobalt-doped maghemite nanoparticles to obtain direct quantitative information on cation distribution as a function of cobalt doping. We found that the distribution of divalent cobalt is stable in the investigated doping range and slightly different from that of bulk, stoichiometric cobalt ferrite. These results confirm that cobalt doping can be used to finely tune the magnetic properties of nanostructured ferrites without modifying their structural integrity.