ищи её в зависимости от того, насколько ты оцениваешь своё понимание платформы

<GridViewColumn Width="300"
                x:Name="docscol"
                Header="документы"
                HeaderTemplate="{StaticResource BooksHeaderTemplate}"
                CellTemplate="{DynamicResource BooksCellTemplate}" />

        <DataTemplate x:Key="BooksHeaderTemplate">
            <DataGrid ItemsSource="{Binding Mode=Default, XPath=./documents}" AutoGenerateColumns="False">
                <DataGrid.Template>
                    <ControlTemplate>
                        <StackPanel>
                            <DataGridColumnHeadersPresenter />
                        </StackPanel>
                    </ControlTemplate>
                </DataGrid.Template>
                <DataGrid.Columns>
                    <DataGridTextColumn Header="type" Binding="{Binding Mode=OneWay, XPath=type}" />
                    <DataGridTextColumn Header="name" Binding="{Binding Mode=OneWay, XPath=name}" />
                    <DataGridTextColumn Header="size" Binding="{Binding Mode=OneWay, XPath=size}" />
                </DataGrid.Columns>
            </DataGrid>
        </DataTemplate>
        <DataTemplate x:Key="BooksCellTemplate">
            <DataGrid HeadersVisibility="None"
                      AutoGenerateColumns="False"
                      ItemsSource="{Binding Mode=Default, XPath=./documents}">
                <DataGrid.Columns>
                    <DataGridTextColumn Binding="{Binding Mode=OneWay, XPath=type}" />
                    <DataGridTextColumn Binding="{Binding Mode=OneWay, XPath=name}" />
                    <DataGridTextColumn Binding="{Binding Mode=OneWay, XPath=size}" />
                </DataGrid.Columns>
            </DataGrid>
        </DataTemplate>

<XmlDataProvider x:Key="MDSource"
                 d:IsDataSource="True"
                 Source="Data/1.xml" />

<DataTemplate x:Key="DocumentosCellTemplate">
    <ListBox  ItemsSource="{Binding Mode=TwoWay, XPath=./documents}" />
</DataTemplate>

<Grid x:Name="LayoutRoot">
    <DataGrid x:Name="list"
              ItemsSource="{Binding Mode=Default, Source={StaticResource MDSource}, XPath=rss/row}"
              AutoGenerateColumns="False">
        <DataGrid.Columns>
            <DataGridTextColumn Header="Фамилия" Binding="{Binding XPath=./family}" />
            <DataGridTextColumn Header="Имя" Binding="{Binding XPath=./name}" />
            <DataGridTemplateColumn Width="300"
                            Header="доки"
                            CellTemplate="{DynamicResource DocumentosCellTemplate}" />
       </DataGrid.Columns>
     </DataGrid>
</Grid>