How to map the bundle/node's field to properties?

Problem/Motivation

How do I specify which entity/node field should be used for a given property?

For example, I have an Event content type with fields (see attached Eventfields.png). I added schema type and properties to the content type (see attached image Eventschema.pdf). I created an Event node (see attached image Eventnode.png). Here's the JSON LD result of an event page in the page HTML head section:

<script type="application/ld+json">{"@context":"https:\/\/schema.org\/","@type":"Event","about":{"@type":"Event"},"duration":{"@type":"Duration"},"endDate":"","image":{"@type":"ImageObject"},"location":"","organizer":{"@type":"Organization"},"performers":{"@type":"Organization"},"startDate":"","eventStatus":"schema:EventRescheduled"}</script>

How do I get the actual info from the node into the JSON data? What did I miss? Your help is greatly appreciated!