How can I find out which presenters have not registered?

When your conference is using Ex Ordo to register your delegates you can keep track of who has not registered through the delegate funnel in the registration hub.

You can message the cold contacts in the funnel who haven't visited your registration hub and also those who delegates who are warm meaning that started to register but haven't paid for their registration yet. The funnel also allows you to message delegates who are unpaid.  

When you click on the message button in the funnel you are transported to the communication hub where you can filter by your delegate's registration status. 

You can also export data to keep track of your delegate registrations using the delegates export.

You can also use filters to check who hasn't registered yet when building your conference programme.

Read here about how to avoid scheduling presentations in your programme with unregistered presenters.