In this work we propose how to identify the location and spatial distribution of Zn vacancies in ZnS quantum dots (QDs). The experiments reveal a peak shift in absorption spectra towards the lower energies (about 0.1 eV) in the presence of Zn vacancies. To explain such a shift we computationally study the absorption spectra when Zn vacancies are localized in the core, on the surface, and both in the core and on the surface of a quantum dot. From the comparison with the experimental data we conclude that the most favorable configuration of the vacancies is an aggregation on a QD surface. We find that Zn vacancies localized in the core or uniformly distributed on the QD surface, do not explain the experimentally observed shift in the absorption curves.