This is the code used to generate the Event Schema for YoastCon

register-graph-piece.php

<?php

/**
 * Adds Schema pieces to our output.
 *
 * @param array                 $pieces  Graph pieces to output.
 * @param \WPSEO_Schema_Context $context Object with context variables.
 *
 * @return array $pieces Graph pieces to output.
 */
function add_graph_pieces( $pieces, $context ): array {
		$pieces[] = new YoastCon( $context );

		return $pieces;
}

add_filter( 'wpseo_schema_graph_pieces', 'yoast_add_graph_pieces', 11, 2 );

yoastcon-graph-piece.php

<?php

use WPSEO_Schema_Context;

/**
 * Class Event
 *
 * @package Yoast\YoastCom\Core\WordPress\Integration\YoastSEO
 */
class YoastCon implements \WPSEO_Graph_Piece {
	/**
	 * A value object with context variables.
	 *
	 * @var \WPSEO_Schema_Context
	 */
	private $context;

	/**
	 * The Event data.
	 *
	 * @var array
	 */
	private $data;

	/**
	 * Event constructor.
	 *
	 * @param WPSEO_Schema_Context $context
	 */
	public function __construct( \WPSEO_Schema_Context $context ) {
		$this->context = $context;
	}

	/**
	 * Determine whether we should output an Event piece.
	 *
	 * @return bool
	 */
	public function is_needed(): bool {
		if ( ! is_page( 1376069 ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Generates our Event data.
	 *
	 * @return array
	 */
	public function generate() {
		$this->data = [
			'@type'            => 'BusinessEvent',
			'@id'              => $this->context->canonical . '#yoastcon',
			'mainEntityOfPage' => [ '@id' => $this->context->canonical . \WPSEO_Schema_IDs::WEBPAGE_HASH ],
			'name'             => get_post( $this->context->id )->post_title,
			'description'      => $this->context->description,
			'organizer'        => [ '@id' => $this->context->site_url . \WPSEO_Schema_IDs::ORGANIZATION_HASH ],
			'startDate'        => date( 'c', strtotime( '24 April 2020 08:00 CET' ) ),
			'endDate'          => date( 'c', strtotime( '24 April 2020 17:00 CET' ) ),
			'url'              => $this->context->canonical,
			'image'            => 'https://yoast.com/app/uploads/2019/10/YoastCon2020-600x338.png',
			'location'         => [
				'@type'   => 'Place',
				'name'    => 'Theater \'t Mozaïek',
				'url'     => 'https://www.mozaiekwijchen.nl/',
				'address' => [
					'@type'           => 'PostalAddress',
					'addressLocality' => 'Wijchen',
					'addressRegion'   => 'Gelderland',
					'addressCountry'  => 'The Netherlands',
					'postalCode'      => '6602 HX',
					'streetAddress'   => 'Campuslaan 6',
				],
			],
		];
    
    return $this->data;
  }
}  

Thanks for the example code. Works perfect.