By default, Januas shows 10 speakers, If you want to edit the display, you need to edit the PHP file metabox-speakers.php in the theme_folder/januas/lib/metaboxes/.
You need to edit the following code in the above file around line number 59.
$speakers_loop = new WP_Query(array( 'post_type' => 'ja-speaker', 'post_status' => 'publish', 'post__in' => $speakers_ids, 'orderby' => 'post__in' ));
You can to change it to
$speakers_loop = new WP_Query(array( 'post_type' => 'ja-speaker', 'post_status' => 'publish', 'post__in' => $speakers_ids, 'orderby' => 'post__in', 'posts_per_page' => 11 ));
By entering 11 in
'posts_per_page' => 11
you will display 11 speakers per page, enter your desired number here.
Be aware that altering the number of speakers may result in misaglinment of the metabox and custom CSS may be needed.