In the database you can check for the package "cmxue" which will have the user exits.
I believe you use option of User Object Registry as well which will be in MDM hub console.
Instead of checking it from backend, you can check it from console.
If you really want it to check from backend, then you can follow above answer.
HUB UserExits can be found in CMXUE package
For IDD userexits export the application and get the JAR.
1) For Oracle databases, all user exit procedures are located in the CMXUE package, if you see under Packages in your ORS schema.
Alternatively, you can also login to hub console -> go to User Object Registry. Here you can view registered user exits, user stored procedures, custom Java cleanse functions, and custom GUI functions for an ORS.
2) IDD user exits can be found as a JAR file if you export the IDD application.