According to the Platform Events Developer Guide, to debug platform events, a developer needs to include the Apex Code and Workflow loglevels in the trace flag entry for the Automated Process entity or the overridden user. The Apex Code log level captures the execution of the Apex trigger that subscribes to the platform event. The Workflow log level captures the execution of the event process or the resumed flow interview that subscribes to the platform event. The other log levels are not relevant for debugging platform events. The Database log level captures database operations, such as DML statements and SOQL queries. The Callout log level captures the details of HTTP requests and responses, such as web service callouts. References: Platform Events Developer Guide, Set Up Debug Logs for Event Subscriptions, Set Up Debug Logging