Two-dimensional (2D) materials have gained prominent attention in the nano-electronics arena, owing to their tunable electronic and optical features. Here, the physical properties of a janus MoSSe monolayer are examined upon the chemically co-doping of S/Se sites by non-metallic and halogen elements (C, Si, N, P, As, and F) employing first-principles calculations. Accordingly, an alteration of both the upper valence and the lower conduction states is revealed for janus MoSSe monolayer upon the replacement of both S and Se anion host atoms by sp-elements (C, Si, N, P, As, and F). A shift in the lowest conduction band underneath the Fermi energy level (EF) occurs in janus MoSSe monolayer when both S and Se elements are replaced by (F, F) atoms. This effectively conducted to a system with an n-type character. In contrast, the highest valence bands moved upward EF owing to the co-doping effect of C, Si, N, P, and As atoms on the janus MoSSe monolayer with p-type nature. The key features of the optical spectra, such as the optical absorption, reflectivity, and electron loss functions of the co-doped janus MoSSe monolayer are inspected. Our results imply a modification in the low-energy photon regime of the co-doped janus MoSSe monolayer at S and Se host atoms by non-metallic sp-elements comparatively to the free-standing monolayer. A reduction in the optical absorption and an increase in the reflectivity at low-energy photon window are detected when the janus MoSSe monolayer is co-doped by (C, Si), (N, P), (P,As), and (F,F) elements, respectively at S and Se chalcogen atoms. The current study infers that the co-doping S and Se sites of janus MoSSe monolayers, with sp- elements, can be beneficial in the future applications of 2D materials for the field-effect transistors and nano-electronic devices.