To clarify grimmy55's response tells you where the C.G. CURRENTLY is, but does not address the original question...

The manufacturer's SUGGEST a C.G. point that is assured of producing a decent flying plane.

If a plane is too tail heavy it will be uncontrollable. This is why you should always START with the manufacturer's recommended C.G.

As Dorsal said, your best approach is to AVOID adding any weight what-so-ever to the plane. The best way to do this but at the same time move or adjust the C.G. "balance point" is to shove things around.

A good candidate is the battery pack since it tends to be relatively heavy.

If your plane is tail heavy, you can move the battery forward.

I put my battery pack in the cowl/nose of my Funtana s90, after I put in a new LIGHTER Saito four stroke engine... this was done to move the C.G. forward.

Likewise I've put my battery pack after of the cowl on a couple of planes that were originally too nose heavy.

If you have NO other recourse and you absolutely MUST add weight ( which should always be the LAST thing you do ) try to add weight as far "out" as possible...

That is, a small 2oz weight at the extreme tail of the plane can offset as much as 8 oz on the nose, because of the long lever moment ( leverage ) it has.

Conversely if you need to add weight to the nose, a great place to put it is in the spinner... dubro sells spinner weights, that have the added benefit of improving engine idle!