Cookies are available via
Request.Cookies collection. To read your custom defined cookies, you can simply do something like this:
if(Request.Cookies["YourKey"]!=null)
{
var myCookie = Request.Cookies["YourKey"].Value;
}
For more information, refer the official documentation here:
How to: Read a Cookie[
^]
If you are trying to access cookies from other websites (e.g search engine websites), then You can't. You can only access cookies sent to your server. You can't read the cookies of other websites, that would be a HUGE security flaws.