The following code is working fine, follow it.
<Grid x:Name="MainGrid">
<Grid.RowDefinitions>
<RowDefinition MinHeight="30" MaxHeight="30" />
<RowDefinition MinHeight="22" MaxHeight="22" />
<RowDefinition Height="155" MinHeight="155" />
<RowDefinition MinHeight="130" />
<RowDefinition MinHeight="25" MaxHeight="25" />
<RowDefinition MinHeight="22" MaxHeight="22" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="360" MinWidth="355" />
<ColumnDefinition MinWidth="330" />
<ColumnDefinition MinWidth="280" />
</Grid.ColumnDefinitions>
<ScrollViewer Grid.Row="3"
Grid.Column="2"
PreviewMouseLeftButtonDown="InnerPanel_PreviewMouseLeftButtonDown_1"
VerticalScrollBarVisibility="Auto">
<StackPanel Name="InnerPanel"
Background="Gray"
IsEnabled="False"
IsEnabledChanged="StackPanel_IsEnabledChanged_1">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="110" />
<ColumnDefinition />
<ColumnDefinition Width="50" />
<ColumnDefinition Width="50" />
<ColumnDefinition Width="20" />
</Grid.ColumnDefinitions>
<Button Grid.Column="2" Content="Inner Panel" />
</Grid>
</StackPanel>
</ScrollViewer>
</Grid>
private void InnerPanel_PreviewMouseLeftButtonDown_1(object sender, MouseButtonEventArgs e)
{
}
This is working fine and implement your logic in the above event.