There are a few ways to do this. One way is to go into the felix console: http://localhost:4502/system/console/bundles, and go under main, and click on the "Sling Resource Resolver" link. Enter the url you want to know more about and press enter. It will give you a list of possible pages it is using. Open up crx/de or the Eclipse plug-in and find the page, and find where the page or template is located.
A quicker way is to add ?debug=layout to the end of the url of the page in question. It will display where every component on your page is located.