for (i = 0; i < dt.Columns.Count; i++)
{
    string Path = dt.Columns[i]....Path;
}

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            foreach (var i in DataGrid.Columns)
            {
                var column = i as DataGridBoundColumn;
                if (column == null) continue;
                var binding = (Binding)column.Binding;
                MessageBox.Show(binding.Path.Path);
            }
        }
    }

<Window x:Class="WpfApplication10.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <DockPanel>
        <StackPanel DockPanel.Dock="Top">
            <Button Width="100" Height="25" Content="Do it" Click="Button_Click"/>
        </StackPanel>
        <DataGrid x:Name="DataGrid">
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding Value1}"/>
                <DataGridTextColumn Binding="{Binding Value1}"/>
            </DataGrid.Columns>
        </DataGrid>
                  
    </DockPanel>
</Window>