Display associated taxonomy child name on single CPT page

To return the list of terms attached to that post, try get_the_term_list(). This will return the terms for a single post and by using the before, separator and after arguments you can easily build an HTML markup structure to suit your needs.

The following example creates an unordered list of terms from the Topics taxonomy attached to a specific post:

<?php
$terms = get_the_term_list( $post->ID, 'topics', '<ul><li>', '</li><li>', '</li></ul>' );
if ( $terms ): ?>
  <h2><?php esc_html_e( 'Topics:', 'yourtextdomain' ); ?></h2>
<?php echo wp_kses_post( $terms, 'yourtextdomain' );
endif;

WP Codex entry for tget_the_term_list():
https://codex.wordpress.org/Function_Reference/get_the_term_list