CG point should be shown in the instructions or described usually as a point of measure back from the leading edge of the wing at the root(right up against the fuselage. for example you may see that the book says the cg is 4.5", that usually means you measure from the leading edge right up against the fuselage back 4.5". That is the recommended CG, yours will be listed somewhere in the manual. I mark that point with a piece of tape or a sharpie on each side of the fuse and then lift the plane up touching only those points. From there you just move things around until the plane balances on those points. Usually on a trainer the CG is right on the main wingspar.