WPF Datagrid

I believe you need to iterating through datagrid.Columns to get the column that you want.

For example below, I use datagrid.Columns[index] to get the checkbox column.

Markup:
<Window x:Class="DataGridCheckBoxColumnTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:DataGridCheckBoxColumnTest"
        Title="MainWindow" Height="350" Width="525" ContentRendered="Window_ContentRendered">
    <Grid>
        <DataGrid Name="datagrid" ItemsSource="{Binding}" AutoGenerateColumns="True"/>
    </Grid>
</Window>

Code:
using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;

namespace DataGridCheckBoxColumnTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new List<Person>
            {
                new Person{Name="Tom", LikeCar = true},
                new Person{Name="Jen", LikeCar = false},
            };
        }

        private void Window_ContentRendered(object sender, EventArgs e)
        {
            DataGridColumn target = datagrid.Columns[1];
        }
    }

    public class Person
    {
        public string Name { set; get; }
        public bool LikeCar { set; get; }
    }
}

William