A barebones WP plugin to add JSON-LD based on post data automatically. It won't really work, but it's a starting point for exploration.

json-ldfy.php

<?php
/*
Plugin Name:  JSON-LDfy
Plugin URI:   https://www.google.com
Description:  Add JSON-LD based on some post data
Version:      1.0
Author:       Martin Splitt
Author URI:   https://www.google.com
License:      GPL2
License URI:  https://www.gnu.org/licenses/gpl-2.0.html
Text Domain:  wtf is this?
Domain Path:  /wat
*/

/*
Stuff above is a mandatory header that WP plugins just want to have.
This "plugin" is probably doing a lot of things wrong, I'm not a WP plugin dev, but it is a starting point.
Let's start with the code that *does stuff*!
*/

function add_jsonld_to_content( $content ) {
  // this will use a global variable called $post which is only available in the loop and in a singular post.
  if( !is_singular() || !in_the_loop() || !is_main_query() ) {
    return $content; // we bail out.
  }
  /*
  The $content is basically the HTML that will show up on the page.
  We append a JSON-LD script to it.
  */
  $content .= '<script type="application/ld+json">
  {
    "@context": "https://schema.org",
    "@type": "NewsArticle",
    "headline": "' . $post->post_title . '", 
    "datePublished": "' . get_post_time( 'Y-m-d\\TH:i:sO' ) . '",
    "author" : [{
      "@type": "Person",
      "name": "' . get_the_author() . '",
      "url": "https://not-sure-how-to-do-this-one.com/lol"
    }]
  }
  </script>';
  return $content; // finally, return it all back to WP to display.
}

// the next line makes WP call our function when the post content is ready to show..
add_filter( 'the_content', add_jsonld_to_content );