How to find which content type is using which context?
Here are some module suggestions that may help get you closer to find the exact answer to your question:


Context Inspector block provided by the Devel module

If you use the Devel module you'll have a "Context Inspector" block. You can place that block in a region on a page and then see the current contexts output via Krumho.
Devel Catcher module

To enhance your "debugging" experience (hm, hm ...), there is also the Devel Catcher module, which has Devel as a module dependency.

Here is an excerpt from its project page (why you may want to consider this module):


  ... aggregates or "catches" all development debug info into one easy to access place.
  
  Similar in style to Firebug or Chrome's Inspector. Devel Catcher intercepts common debug info into a tabbed interface as opposed to having to assign debug blocks to a region or dumping the output at the end of your HTML document.
  
  Currently Devel Catcher can catch the query log from the Devel module, node access rules from the Devel Node Access module and the context inspector block from the Context UI module.



So by using (repeating) this approach for a page of each of your content types, you might be able to find out which content type is using which context, no?