CNAME record is important for adding the custom domain in your blogger blog URL. To redirect blogger subdomain (yoursite.blogspot.com) to you registered custom domain (yoursite.com) it required to add CNAME entries to your domain DNS of your domain registrar account. You will easy find CNAME record first time when you will try to add custom domain on blogger where first CNAME is same for all blogspot account and second CNAME is unique for the account and for the domain.
But if you lost it then how to get that unique CNAME record next time? Let’s see how to get that unique cname record next time after you lost it. At first you have to go google webmaster verification section. You can go there by this link. After login on your webmaster account with same gmail acccount you used to create blog, you will see there your all blogs and domains you added on your blogspot blog.
Then click on Verification details on the right for that domain you want to get CNAME. After click verification details you will be redirected to next page. In the bottom of that page you will see Verified owners section.
In the below verified owners section you will see your email address you used for that blog and in right hand side you will see Verification details like at image. When you click on it you will get a popup page with your blog unique CNAME record like below:
In this popup page id in left is host and id in right is point to address. Now you just copy your unique and add it again on your domain service provider account. Now your domain is pointed on your Blogspot blog.
Hope you are now able to get your existing CNAME record if you lost it. Happy Blogging.