Bloggers, and web site owners, that have more than one domain name may be surprised to learn that they cannot track their AdSense statistics automatically.
Google purchased a web site statistics company called Urchin many years ago, and turned it into a free service called Google Analytics. Last year Google made it possible to link your AdSense account to Google Analytics. Domain name owners who had a single domain name, as well as owners of multiple domain names, linked their domains to Google Analytics so their AdSense traffic could be tracked, but there is an extra step that owners of multiple domain names may have missed.
First let’s check to see if Google Analytics is tracking your AdSense traffic. Go to the Google Analytics home page and login. You should see your domain name listed, so click the View report link.

Expand the menu on the left to reveal Content. If you see AdSense listed, then your AdSense account is properly linked to Google Analytics, if not you’ll need to link your Adsense account before continuing. If you see AdSense listed on the menu click it. If you see mostly zeroes where there should be statistical data on the right, then you’ll need to go another step for your AdSense data to be tracked for this domain name.

Go back to the Google Analytics home page, and to the right of the View reports link you’ll see an Edit link. Click the Edit link, and you should now be at your Profile Settings page.

Listed on this page you will see the category AdSense Data. If your blog or web site are setup correctly then you’ll see Receiving AdSense data. If you don’t see Receiving AdSense data, then you’ll need to continue to the next step.

To the right of Main Website Profile Information you’ll see an Edit link, which you should click now. You should now be at the Edit Profile Information page.

If this domain name is not the primary domain name (web site) for the account, and it is an additional domain name you will see AdSense Data. If it is not already, then check the box. Now you’ll need to copy the script in the box, and paste it into your web site pages. Although the instructions here say you can paste the script into the "top" of any webpage, it is critical that you paste the code in the correct spot, because how your AdSense and Google Analytics scripts are ordered in your web pages will determine if AdSense and Google Analytics record your information accurately.
The order with which to place Google scripts in your website is explained here.
The correct place to paste the AdSense Analytics Code (ASAC) below is immediately after the tag, which is usually in your header template if you have a blog. The ASAC must be placed above the AdSense ad code and Google Analytics Tracking code for your AdSense account to be properly applied to multiple domains.
The AdSense Analytics Code (ASAC) is made up of three parts:

User Account

User Account Number

Property Index Number

The primary domain name, or web site, for the Google Analytics account will not require a AdSense Analytics Code (ASAC). The primary web site will only require the Google Analytics code, and Google AdSense code, if you’re running Google ads.