The index.log file, located in
/opt/searchblox/webapps/searchblox/logs (For Linux)
contains information on all of the files that have been indexed and skipped. Please check the same for more information.
If you want to check a specific URL/file whether it has been indexed in the collection, you can check the same using the Documents tab. Please give the URL and click the status button to check whether the URL/file has been indexed
Note: This is applicable only for HTTP and File Collection.