Google has added a new feature to Webmaster Tools called the Structured Data Dashboard. The purpose, Google says, is to provide webmasters with more visibility into the structured data that Google knows about for their site.
It comes with three views, which will let you see things like:
The first view is Site-level view, which aggregates data by root item type and vocabulary schema. "Root item type means an item that is not an attribute of another on the same page," Google's Webmaster Tools team explains. "For example, the site below has about 2 million Schema.Org annotations for Books."
The second view is Itemtype-level, and provides per-page details for each item. "Google parses and stores a fixed number of pages for each site and item type," the team says. "They are stored in decreasing order by the time in which they were crawled. We also keep all their structured data markup. For certain item types we also provide specialized preview columns as seen in this example below (e.g. 'Name' is specific to schema.org Product)."
The third view is Page-level view, which shows all attributes for each item type on a given page.
As the company notes, you can use the dashboard to verify that Google is picking up any new markup, or discover any issues Google may be having with old markup.