As per the below link of salesforce release notes, we can now see the attendee list on the event object in the lightning experience without enabling setting up the lightning sync.
Salesforce Release notes: https://releasenotes.docs.salesforce.com/en-us/spring19/release-notes/rn_sales_productivity_calendar_attendees.htm
I'm testing this functionality on my Spring 19 enabled Org. But, I'm not able to see the attendee list on the event object in lightning experience. Is there any other configuration setting needs to be done?
Attendees field to the page layout for events
as mentioned in documentation, I was able to see the Attendees in lightning without any additional setup. You are looking at wrong page layout where attendees is not added?