Given that we can run an analysis to identify these meetings before your migration you have your choice of informing your users about specific meetings (to make it as easy as possible), or handling it afterwards. Both is probably good.
Easiest way to find them post-migration is to search on the "Meeting_MissingOrganizer" category in Outlook.
But if you are using Office 365 or on-premises via OWA instead of Outlook there's no easy list display.
You can can however find all of these visually using categories.
So set a specific color looking for the category we added on insertion, as so:
Again, better to get the word out to your users before the migration and get them used to the way things work in Exchange as opposed to Oracle Calendar Server, but we're all about the reality of the situation.