How to put this result inside that result?

Run the loop in advance and populate an array, which in turn you include in the $result afterward.

<?php
 // Create an empty array
 $comlistall = array();

 foreach ( $comments as $comment ){
   $comlistall[] = $comment; // <= Populate the array with the comments in the loop
 };

 $rtitlez = get_the_title();
 $rimgz = get_the_post_thumbnail_url(get_the_ID(), 'full');
 $rvaluez = get_post_meta($post->ID, 'comments_rating_value', true);
 $rcountz = get_post_meta($post->ID, 'comments_rating_count', true);

 $result = [
  "@context" => "https://schema.org/",
  "@type" => "Organization",
  "name" => $rtitlez,
  "image" => $rimgz,
  "aggregateRating" => [
        "@type" => "AggregateRating",
        "ratingValue" => $rvaluez,
        "bestRating" => "5",
        "worstRating" => "1",
        "ratingCount" => $rcountz
      ],
   "comlistall" => $comlistall, // insert the comment array in your $results array
  ];
?>
<script type="application/ld+json"><?php echo json_encode($result); ?></script>

Update

If you only want certain attributes from the comments, simply create your own array with the attributes you want. In this example $comment is an array with the attributes. Modify to your needs.

// ...
foreach ( $comments as $comment ){
  $c = [
    "@type" => "Review",
    "headline" => $comment["headline"],
    "reviewbody" => $comment["reviewbody"],
    "datePublished" => $comment["datePublished"],
    "itemReviewed" => [
       "@type" => "Organization",
       "name" => $comment["name"],
    ],
    "author " => [
       "@type" => "Person",
       "name" => $comment["authorname"],
    ],  
  ];

  $comlistall[] = $c;
};
// ...