How do I insert JS tracking code to a page with the WP editor?

by

Use conditional tags.

Change the 5th parameter to load in the footer.

Change get_stylesheet_directory_uri() to get_template_directory_uri() for use in parent themes.

add_action( 'wp_enqueue_scripts', 'add_tracking_scripts' );

function add_tracking_scripts() {
if ( is_page('slug') ) {
wp_register_script(
    'tracking-script',
    get_stylesheet_directory_uri() . '/tracking-script.js',
    false,
    '1.0',
    true
);

wp_enqueue_script( 'tracking-script' );
    }
}

Source http://codex.wordpress.org/Function_Reference/wp_enqueue_script