Question

if axis of rotation passing through center of mass , in that case radius of gyration is what

Answer 1

do you know what radius of gyration means?

Answer 2

If you are a mechanical engineering student then u'll mostly be using the formula r = (I/m)^.5
where I is moment of inertia about the axis. So now, all you need to know is the moment of inertia about the axis of rotation, which in your case is the center of mass of the body and so its very easy to calculate. If its a disc then I = (mr^2)/2, similarly you can calculate I for other bodies also. I guess you can find "I" on your own.