If I had to guess, I would say he's looking for the ID for the web part
page that the DVWP resides upon. Presumably for some way to identify active
content with a page library, maybe?

the page id (id column) in the pages library.

If you've added a DVWP to a DispForm or EditForm and are looking for the ID of
the list item, it's pretty straightforward:

1. Hover over the DVWP and click the chevron that appears,
2. Click Web Part Parameters,
3. Add a parameter with a source of QueryString and field of ID

Now, you'll have a ParameterBinding and an xsl:param that will provide you with
the ID of the list item.

If you meant something else, either from the URL or elsewhere, reply with more
detail and we can help you figure it out. If you need to post code somewhere,
try SPOverflow or EUSP's Stump the Panel; then post the link back here in the
group.