When an object is thrown into the air, different parts of the object can follow complicated paths if the object spins as it travels. However, the center-of-mass of the object will always follow a parabolic trajectory through the air.

The center-of-mass is the point that moves as though all the mass is concentrated there.

The center-of-mass of an object, or a collection of objects, can be found using:
Xcom =
x1m1 +x2m2 + ...
m1 + m2 + ...

That tells you the x-coordinate of the center of mass. The y-coordinate and z-coordinate can be found from equivalent expressions.

If you have mass distributed in some way over an object instead of having a number of discrete masses, it's generally necessary to integrate to find the center of mass. The integral equation looks like:
Xcom =
x dm
x dm
      where M is the total mass of the object