Kazkas tokio tada bus:

public event OnDoSomething;

public string Propertis 
{
    get 
    {
        return _PropercioAttribute;
    }
    set 
    {
        if(OnDoSomething!=null)
        {
            OnDoSomething(this, new EventArgs());
        }
        _PropercioAttribute = value;
    }
}