I want textblock value but could not able to do that

Question

       <Grid>
    <GroupBox  FontSize="16" FontWeight="Bold" Header="Testing" 
       BorderBrush="Orange" BorderThickness="3">
        <DataGrid Background="Transparent">
            <DataGrid.Columns>
                <DataGridTemplateColumn Width="Auto">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Grid IsEnabled="True" Background="Transparent">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="Auto"/>
                                    <ColumnDefinition Width="Auto"/>
                                </Grid.ColumnDefinitions>
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="Auto"/>
                                    <RowDefinition Height="Auto"/>
                                </Grid.RowDefinitions>
                                <TextBlock  Text="Hello" Width="50" HorizontalAlignment="Center" VerticalAlignment="Center" 
                                           ToolTipService.ToolTip="Testing" Background="Aqua" ToolTipService.IsEnabled="True" 
                                           ToolTipService.ShowOnDisabled="True" IsEnabled="True" Height="20" >
                                </TextBlock>
                            </Grid>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
    </GroupBox>
</Grid>

Here is my XAML and this datagrid also comes under groupbox . I have tried many approach but couldnt figure it out . I want to show textblock value.