<dxb:BarButtonItem Name="bOpen" Content="Открыть" 
                            Hint="Открыть план" ItemClick="bOpen_ItemClick" >
</dxb:BarButtonItem>

<dxb:BarButtonItem Name="bOpen" Content="Открыть" 
                            Hint="Открыть план" ItemClick="bOpen_ItemClick" >
</dxb:BarButtonItem>

<navigation:Frame x:Name="Frame" />
<HyperlinkButton Click="HyperlinkButton_Click" Tag="/Page_add.xaml" Content="Page"/>

   private void HyperlinkButton_Click(object sender, RoutedEventArgs e)
        {
            HyperlinkButton btn = sender as HyperlinkButton;
            string url = btn.Tag.ToString();
            this.Frame.Navigate(new Uri(url, UriKind.Relative));
        }

<Button Content="Button" Height="23" Name="button" Width="75" Click="button_Click" />

<navigation:Frame x:Name="Frame" />

 this.Frame.Navigate(new Uri("/Page_add.xaml", UriKind.Relative));   

Control_Plan.Focus();

     private void AddItem_ItemClick(object sender, DevExpress.Xpf.Bars.ItemClickEventArgs e)
        {
            Child_add add = new Child_add();
            add.Show();   
        }

   public Child_add()
        {
            InitializeComponent();
            this.Frame_add.Navigate(new Uri("/Plan/Page_add.xaml", UriKind.Relative));
        }

<sdk:Frame HorizontalAlignment="Left" Name="frame" VerticalAlignment="Top" />

    private void button1_Click(object sender, RoutedEventArgs e)
        {
            Child_Window add = new Child_Window();
            add.Show();
        }

    public Child_Window()
        {
            InitializeComponent();
            this.frame.Navigate(new Uri("/Plan/Page_add.xaml", UriKind.Relative));
        }

    private void button1_Click(object sender, RoutedEventArgs e)
        {
           this.frame.Navigate(new Uri("/Plan/Page_2.xaml", UriKind.Relative));            
        }

<sdk:Frame Height="100" HorizontalAlignment="Left" Margin="108,113,0,0" Name="frame1" VerticalAlignment="Top" Width="200" />

   private void button1_Click(object sender, RoutedEventArgs e)
        {
            ChildWindow_1 add_1 = new ChildWindow_1();
            add_1.Show();
        }

   public ChildWindow_1()
        {
            InitializeComponent();
            this.frame1.Navigate(new Uri("/Plan/Page_2.xaml", UriKind.Relative));
        }

            this.frame1.Navigate(new Uri("/Plan/Page_2.xaml", UriKind.Relative));

            this.frame1.Navigate(new Uri("/Plan/Page_2.xaml", UriKind.Relative));