Single page Template for pages that begin with ‘confirmation-‘

We can make use of the page_template filter to achieve this. All we need to do is to make sure that confirmation is the first word in the page page title

add_filter( 'page_template', function ( $template )
{
    // Get the current page object
    $post = get_queried_object();

    /**
     * Get the first instance of confirmation, if it is not 0, bail
     * We will be using the page name, which is the slug
     */
    if ( 0 !== stripos( $post->post_name, 'confirmation' ) )
        return $template;

    // We have confimation as first word, lets continue
    $locate_template = locate_template( 'page-confirmation.php' );

    // Check if $locate_template is not empty, if so, bail
    if ( !$locate_template )
        return $template;

    // page-confirmation.php exist, return it
    return $locate_template;
});