I dont think you will be able to view checkout docs under the sites/docs lib. Reason for this is if you want to see all the checkout docs then you have to walk into each site and goto site actions--> "Manage content and structures" and looking for all checkout doc which is available at the individual site level but not at the farm level to view all sites checkout docs.
(OR)
Try with evenhandlers or featue to fetch all the check out doc under the web application level.
