How many number of atoms are there in a cube based unit cell having one atom on each corner and two atoms on each body diagonal of cube?

There are four body diagonals. Atoms on the body diagonals are not shared by any other unit cell.

Contribution by atoms on corners $=8\times \frac{1}{8}=1$

Contribution by atoms on body diagonal = 2 x 4 = 8

$\therefore$    Total number of atoms = 1 + 8 = 9.