New column in the Administration > Users default view

If you want to add some column to the user list in the User app (module), then you need to create a custom extender for the Users module. Something like described in the documentation on extenders.
The class name you need to adjust is UserListExtender. This class has a method in which the columns are registered:

public override void OnInit()
{
    string[] columns = {
        "UserID",
        "UserName",
        "FullName",
        "Email",
        "UserNickName",
        "UserCreated",
        "UserEnabled",
        @"(CASE 
            WHEN UserPassword IS NULL OR UserPassword = '' THEN 0 
            ELSE 1 
            END) AS UserHasPassword",
        "UserIsExternal",
        "UserIsDomain",
        "UserPrivilegeLevel"
    };
    Control.Columns = columns.Join(", ");
    //...
}

So, you need to create a custom extender which will add required column into that list, for example:

using CMS.Membership.Web.UI;
[assembly: CMS.RegisterCustomClass("MyListExtender", typeof(CustomCode.MyListExtender))]
namespace CustomCode
{
    public class MyListExtender : UserListExtender
    {
        public override void OnInit()
        {
            base.OnInit();
            Control.Columns += ", LastLogon";
        }
    }
}   

And now you just need to adjust the UI to use your extender. Go to Modules application > Users > User interface and then find the Users UI elements as shown on this screen shot and on the Properties tab click the Customize button to edit the settings and select your extender.