Refer to the arrangement of charges in figure and a Gaussian surface of radius R with Q at the centre. Then, 

Gauss' law states that total electric flux of an enclosed surface is given by $\frac{\mathrm{q}}{{\epsilon }_{\circ }}$ , where q is the charge enclosed by the surface. Thus, from figure,

Total charge inside the surface is = Q - 2Q = -Q 

$\therefore$Total flux through the surface of the sphere $=\frac{-\mathrm{Q}}{{\epsilon }_{\circ }}$

Since -2Q is not at the centre of the Gaussian surface , field produced by -2Q at different points on the Gaussian surface will be different .