That's actually not used or at least it's used for something very specific that doesn't apply to your case.
You will have to add it to multiple templates. You can get the content template name by looking for a specific class name in the CSS.
For example while viewing media you will see an element that has a class "xengallery_media_view" therefore the template you would need to add the noindex code to is "xengallery_media_view".
Make sure you do it in the proper supported way. We noindex a few pages so search templates for "noindex" for the correct code to use (it needs to be wrapped in a special xen tag to put it up in the header).