If ironizzy is configured properly on the new T2 Macs, you should be able to enter the Recovery Key by clicking on the "[?]" icon and then the right-pointing arrow after the words "Recovery Key" as shown below:

If you are not getting that dialog when you click on the icon, you can reset this by the following steps:

1. Have the user unlock the disk and log into their account
2. Go to System Preferences → Profiles.    Confirm there is an "Enable FileVault" profile in the list of profiles.  If not, stop here and reach out to Mac Engineering.
3. Run the following command:   sudo fdesetup changerecovery -personal
   
   1. enter the user's uniqname where it says "Enter the user name:"
   2. enter their password at the next prompt
   3. This will show you a personal recovery key – you do not need to write this down.
4. Run this command after that:  sudo jamf recon
5. Run this command after that:  diskutil ap updatePreboot /
     (do not forget the trailing /)
6. Reboot the computer

That should give you the Recovery Key option after the reboot.  

8-23-18:  If you need the Recovery Key after that, please contact the Mac Engineering team.   As of this date, the Recovery Key is not published to the computer's izzy record.