How to expose participant information to the event's trainer?
From my limited knowledge of the module, this sounds like the perfect use case for CiviCRM Entity.

You should be able to add an entity reference field to the Event entity (that CiviCRM Entity would create), the Participants entity (I think that CiviCRM Entity would create) and one to the Trainer Content Type (that you'd create) and link them together.

From there, you should be able to create whatever View you want with logged on user as the contextual filter.