In 1.9-- you use getTicksSincelastAttack but things changed and I don't know how anymore.

        // TODO: find better attack animation method
        int ticksSinceLastAttack = dragon.getLastAttackedEntityTime(); 
        
        boolean jawFlag = (ticksSinceLastAttack >= 0 && ticksSinceLastAttack < JAW_OPENING_TIME_FOR_ATTACK);
        jawTimer.add(jawFlag ? 0.2f : -0.6f);
        jawTimer.set(0.0F);

When I use the code above it just open closes the mouth of the dragon even when not attacking.

If no one cant understand unless tell me how other mobs use animations when attacking, show me where the classes where their animations are handled.

Well, you can easily just create a counter yourself. Set it when the entity attacks, decrement it each tick in an update method, and us it in the render or model code to rotate the mouth or other thing you want to animate.