Pretty much impossible unless you have already have all that documented outside the EBS system. You can of course get anything registered to the custom app top, however you cannot guarantee that a standard object has not been modified (unless it's been flagged in the application).
You have to make list/inventory of all customization done on your Prod environment so that you can take care during the upgrade.
below are the standard reports which can give you differences of EBS versions and this will help you to focus your efforts on the areas which are required.
EBS ATG Seed Data Comparison Report (Doc ID 1327399.1)
EBS File Comparison Report [VIDEO] (Doc ID 1446430.1)
EBS Data Model Comparison Report Overview (Doc ID 1290886.1)
These 3 notes are very good and helpful for your upgrade project.