To define stiffness of a structure, you need a good definition of the fixed surface and the moving surface, and the direction you are moving that surface.
It looks like you have a 2x2x2 cell cube.
Hold the entire bottom face of the cube fixed, and apply -0.1 mm displacement on the entire top face of the cube. Insert a Reaction Force Probe on the Displacement. The stiffness of the 2x2 cell cube is the Force divided by 0.1 mm. It looks like a symmetric structure, so the stiffness in the X, Y and Z directions would all be equal. That takes care of the axial stiffness.
If you want to know about shear stiffness, then you have to take the top face and apply a sideways force. Here is the definition of Shear Modulus. https://en.wikipedia.org/wiki/Shear_modulus
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