I have a 20 ft. cat with wingmast ....and with more weather helm;

The issue is if moving the draft forward then reduces also the weather helm for the fact that moves also the CE forward.

The short answer is "yes" the CE will move forward, but by a shorter distance than that of the draft movement.

The difference is due to the jib, obviously, and due to more complex aerodynamic reasons that I will leave for someone more qualified to explain.

I would only move the draft to move the CE if the sail would also perform better after the change. Otherwise, just change the mast and/or rudder trim, as already suggested.

move the tip of the blade forward resolve the problem or hide the problem ?

The draft now is at 40% and i not consider the wingmast ..... i think that if the draft move to 30% the sail perform better ..... or not ?

Tilting the rudder forward solves the problem and reduces the possibility of ventilation.
If the mast is vertical, I would tilt the rudder forward as much as possible and then rake the mast back until the rudder feels right.
A totally neutral helm is not ideal, so don't try to completely eliminate weather helm.

....... and move also the CE forward ?
..... and it reduces the weather helm ?

The wingmast is part of the airofoil and must be considered. If it is a 10% wingmast, the airfoil draft is at 50% and moving it forward should be beneficial.

Still, it depends on other factors. Best thing to do is check the draft position of the regatta winners in your class.

A few relevant questions:
What boat is it?
Does the jib overlap?
Do you use a downhaul? Is it powerfull enough?
How old are your sails and of what sailcloth?
Are the battens not tappered at all or you just plan to increase the tapper?

...i don't understand the rule for which if I move the rudder forward i reduces the weather helm. please explains me.

It does not look natural, but tilting the rudder forward may improve its balance, depending on how it is now. I'll try to find a drawing.