The head tag is in the page/elements/head view.  Extend the view and you can add your code.

Is it just a copy and paste thing? We got a fatal error after we pasted the code under the last line.

@usac

1 - Create your own theme/plugin

2 - Create a new file in your plugin:

/mod/your_awesome_plugin/views/default/adsense/head.php

3 - Edit this file with your above AdSense code:

<?php ?>

<script>...</script>

4 - Add the followed code in your start.php between init() function:

elgg_extend_view('page/elements/head', 'adsense/head');

5 - Flush the caches via Administration

Learn Elgg