If a charged sphere is in uniform electric field then find the net flux through it?

The net flux will be zero. The electric field lines have the same intensity at every point of the sphere because the field is completely uniform. Every electric field line entering the sphere at any point along the surface of the half of the sphere that is facing the field source will be cancelled out by an electric field line exiting the sphere at the corresponding opposite point on the surface of the opposite half of the sphere that is facing away from the field. So, every field line entering will be cancelled by a field line exiting, and the net flux of the lines will be zero.