Я использовал привязку для передачи FocusManager.FocusedElement в качестве параметра.
<Button Cursor="Hand" x:Name="NetworkModel" Width="Auto" Height="Auto" Background="Transparent" BorderBrush="Transparent" Foreground="#FF0398E2"
Command="{Binding Path=MenuSelectCommand}" CommandParameter="{Binding ElementName=root, Path=(FocusManager.FocusedElement)}">
<Grid Width="145">
<materialDesign:PackIcon Kind="GraphOutline" VerticalAlignment="Center"/>
<TextBlock HorizontalAlignment="Center" Text="Network Model" FontFamily="Champagne & Limousines"/>
</Grid>
</Button>
И работает как надо. Теперь я создал Меню, но Параметр Команды нулевой. Кто-нибудь знает, почему не работает для кнопки в меню, но работает только для кнопки за пределами меню.
<Menu FontSize="14" VerticalAlignment="Center" Background="#FF303030" FontFamily="Champagne & Limousines" Foreground="#FF0398E2" HorizontalAlignment="Center" Height="28" FontWeight="Bold">
<MenuItem Background="#FF303030" Height="28" Width="Auto">
<MenuItem.Header>
<Grid Width="Auto">
<materialDesign:PackIcon Kind="ViewGrid" VerticalAlignment="Center"/>
<TextBlock Width="Auto" Text="Summaries" VerticalAlignment="Center" HorizontalAlignment="Center" Margin="20,0,0,0"/>
</Grid>
</MenuItem.Header>
<Button Cursor="Hand" x:Name="SignalsSummary" Width="Auto" Height="Auto" Background="#FF303030" BorderBrush="Transparent" Foreground="#FF0398E2"
Command="{Binding Path=MenuSelectCommand}" CommandParameter="{Binding ElementName=root, Path=(FocusManager.FocusedElement)}">
<Grid Width="145">
<TextBlock HorizontalAlignment="Center" Text="Signals Summary" FontFamily="Champagne & Limousines"/>
</Grid>
</Button>
<Button Cursor="Hand" x:Name="EventSummary" Width="Auto" Height="Auto" Background="#FF303030" BorderBrush="Transparent" Foreground="#FF0398E2"
Command="{Binding Path=MenuSelectCommand}" CommandParameter="{Binding ElementName=root, Path=(FocusManager.FocusedElement)}">
<Grid Width="145">
<TextBlock HorizontalAlignment="Center" Text="Event Summary" FontFamily="Champagne & Limousines"/>
</Grid>
</Button>
<Button Cursor="Hand" x:Name="LoggesSummary" Width="Auto" Height="Auto" Background="#FF303030" BorderBrush="Transparent" Foreground="#FF0398E2"
Command="{Binding Path=MenuSelectCommand}" CommandParameter="{Binding ElementName=root, Path=(FocusManager.FocusedElement)}">
<Grid Width="145">
<TextBlock HorizontalAlignment="Center" Text="Logges Summary" FontFamily="Champagne & Limousines"/>
</Grid>
</Button>
</MenuItem>
</Menu>