Confluence Cloud added a plugins usage screen at https://YOURSITEURL.atlassian.net/wiki/admin/pluginusage.action (replace YOURSITEURL with the sub domain of your Confluence instance). 


For Confluence Server 6.x navigate to baseUrl/admin/pluginusage.action. (Replace baseURL with the base URL of your Confluence instance).

Click the draw.io entry (which shows the number of diagrams) to obtain a search generated list of pages with draw.io diagrams on.


To list draw.io diagram attachments, baseUrl/label/drawio.