Plone is very flexible. Unfortunately, this implies that often different solutions exist for the same problem and it is not necessarily straight forward to find out how/where a given case is handled.
In general, there are two cases:
- what you look for is in the file system
- what you look for is in Zope's (or even an external) database
To check 1), I would look at the HTML source code of your page, determine key strings and make a recursive search over the sources to find the implicated artefacts.
One uses 2) mainly for content (your description does not directly indicate that your observation come from content) and for customizations. You can find many customizations via the ZMI (= "Zope Management Interface") in the object
portal_view_customizations (that is the typical place for customized scripts/templates/views). Unfortunately, custom scripts or templates can be stored anywhere in the Zope database;
portal_view_customizations is just the typical place. Let's hope that this is not your case.