Getting comments of an specefic user

You could try this way:

<?php
$my_user = get_current_user_id();
$args = array(
    'post_type' => 'custom-post-type',
    'user_id' => $my_user,

);
$comments = get_comments($args);
foreach($comments as $comment) :
    echo($comment->comment_author . '<br />' . $comment->comment_content);
endforeach;

?>

Provided that your user has comments!!