Page content differs from editor
It depends on how the developer did on the website. It could be very difficult if it is done by a developer who is not familiar with Drupal. For your situation, I can share some possible places of code for your reference.

Drupal developer may do it in:


Preprocess function in theme template.php
Field pre render function in custom module.


PHP developer may do it in:


PHP condition code in node.tpl.php


Frontend developer may do it in:


DOM manipulation in theme js file.