There are huge number of function modules which are called in one order runtime as event callback.

If you want to research by yourself, set a breakpoint on the function module below, which is a central entry point to call event handler function module:

# How to find given function module by event name

use tcode CRMV_EVENT, specify object name and event name, F8

In my example, the function module CRM_PRODUCT_I_A_CHANGE_ORGM_EC I observed in the debugger appears as the first row in the result: