Storing content into a custom taxonomy

Your question is confusing but assuming that you want your array to be an argument set for, say, wp_insert_post() then…

I am wondering how I can include it into the array for posting with
the content from the string provided in the example.

… you need tax_input. I am pretty sure I’ve got this right:

$my_post = array(
  'post_title'    => wp_strip_all_tags( trim( $post_title ) ),
  'post_content'  => $my_post,
  'post_status'   => 'publish',
  'post_author'   => 2,
  'post_category' => array( 2 ),
  'tax_input' => array(
    'genre' => 'abcdefg',
  ),
  'post_date' => date('Y-m-d H:i:s')
);