Efficient sensing of sulfur containing toxic gases like H2S and SO2 is of outmost importance due to the adverse effects of these noxious gases. Absence of an efficient 2D based nanosensors capable of anchoring H2S and SO2 with feasible binding and an apparent variation in electronic properties upon the exposure of gas molecules has motivated us to explore the promise of germanene nano sheet (Ge-NS) for this purpose. In the present study, we have performed a comprehensive computational investigation by means of DFT based first principles calculations to envisage the structural, electronic and gas sensing properties of pristine, defected and metal substituted Ge-NS. Our initial screening has revealed that although interaction of SO2 on pristine Ge-NS is within the desirable range, however H2S binding is falling below the required values to guarantee an effective sensing. To improve the binding characteristics, we have considered the interactions between H2S and SO2 with defected and metal substituted Ge-NS. The systematic removals of Ge atoms from a reasonably large super cell lead to mono-vacancy, di-vacancies and tri-vacancies in Ge-NS. Similarly, different transition metals like As, Co, Cu, Fe, Ga, Ge Ni and Zn have been substituted into the monolayer to realize substituted Ge-NS. Our van der Waals corrected DFT calculations have concluded that the vacancy and substitution defects not only improve the binding characteristics but also enhance the sensing propensity of both H2S and SO2. The total and projected density of states show significant variations in electronic properties of pristine and defected Ge-NS before and after the exposure to the gases, which are essential in constituting a signal to be detected by the external circuit of the sensor. We strongly believe that out present work would not only advance the knowledge towards the application of Ge-NS based sensing, but also provide the motivation for the synthesis of an efficient nanosensors for H2S and SO2.