Find the method which AJAX GET calls

If the url is something like this admin-ajax.php?example_ajax_request=1&data=1234

The add_action function in the code would be wp_ajax_nopriv_example_ajax_request

So, try to grep the whole of your theme directory or plugin directory for the text.

Example: grep -r 'wp_ajax_nopriv_example_ajax_request' *

The second parameter of the add_action is the function name you’re looking for.

See https://codex.wordpress.org/AJAX_in_Plugins#Ajax_on_the_Viewer-Facing_Side for example of how it works.