A call to method `getChildHtml()` loads the HTML for the child block with the name which is passed to the method, so in this case we are looking for a child block named *right*.
To determine where to find this child block we need to know which block is calling this method. I know that that particular call to the `getChildHtml()` method appears in the main page column template as *right* is one of the columns. So have a look in the `page.xml` layout file and search for the template file inside which you found the method call, you will find something like this:
<reference name="root">
<action method="setTemplate"><template>page/2columns-right.phtml</template></action>
<!-- Mark root page block that template is applied -->
<action method="setIsHandle"><applied>1</applied></action>
</reference>
Using the `<reference>` tag in a layout file allows you to alter the targeted block, and the `<action>` tag allows you to run a block method inside the block you are working with. So this section of layout sets the template inside the *root* block. From this we know that it is the *root* block calling the `getChildHtml()` method.
Next lets look at where the *root* block is defined in the layout, it's in the same `page.xml` layout file, and should be right near the top:
<block type="page/html" name="root" output="toHtml" template="page/3columns.phtml">
...
<block type="core/text_list" name="right" as="right" translate="label">
<label>Right Column</label>
</block>
...
</block>
There is quite a lot defined in this block, but you can see that it is given the name *root* and defines quite a few child blocks. One of these child blocks is named *right* and it is this block whose HTML is being output by the `getChildHtml()` method. It is important to note the block type - `core/text_list`. This is a special block type which means that when rendering out the HTML for this block using the `getChildHtml()` method, child blocks will also be rendered. If the block type was `page/html` like with the root block, every child block added to the *right* block would need it's own `getChildHtml()` method call, using this block type, you only need a call to `getChildHtml('right')` and all child blocks will also be rendered.
As you can see the *right* block is defined here but it is empty. This is because in exactly the same way as your have the tag referencing the root block (`<reference name="root">`) other layout files add child blocks to the *right* block by referencing the *right* block.
<reference name="right">
...
</reference>
So to finally answer your question (and hopefully inform a little along the way), you need to be looking in layout files other than `page.xml` for references to the *right* block, here you will find all of the child content output by the `getChildHtml()` method call.
You can alter what is added to the *right* block in your own module layout file, or `local.xml` layout file if you are not creating a module. I briefly cover the `local.xml` layout file in my answer [here][1] with example syntax to add new blocks and remove blocks added in other layout files.
[1]:
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