What will happen to gravity on surface if the mass of earth gets evenly shifted to crust leaving center hollow?
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$\begingroup$ You will not notice en.wikipedia.org/wiki/Gauss%27s_law_for_gravity $\endgroup$– user126422Commented May 9, 2017 at 12:28
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Nothing.
It follows directly from Gauss Theorem for gravity (better known as Divergence Theorem) that as long as the test mass is outside of the Earth (surface is outside, right?), it does not matter whether it is hollow or not.
You might find it interesting that because of the same theorem, the gravitational force inside the hollow Earth is zero, as any Gaussian surface placed in there does not enclose any mass.
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2$\begingroup$ Note that the rotation of Earth would be affected, however, because the change in the Earth's moment of inertia would be non-trivial on that scale. $\endgroup$– CoilKidCommented May 9, 2017 at 13:07