Style="{StaticResource FeatureDataGridStyle1}"Solved! Go to Solution.
GraphicsLayer="{Binding Layers[FeatureLINES; FeaturePOINTS; SelectGraphicLayer], ElementName=Map}"
you can change it at run time if you need (but only one at a time).
<TextBlock x:Name="PathLayer" Text="" Visibility="Collapsed" FontWeight="Bold" Foreground="WHITE" FontSize="10" VerticalAlignment="Center" />
<esri:FeatureDataGrid Grid.Row="1" x:Name="FeatureDataGrid" Height="170"
Map="{Binding ElementName=Map}"
GraphicsLayer="{Binding Text, ElementName=PathLayer, Mode=OneWay}" Style="{StaticResource FeatureDataGridStyle1}"/>