If you’re the parent theme Developer, you can add the hook in your parent themes file and then use it in a custom function in your child theme.
1. Add Hook To Parent Themes File
<?php do_action( 'after_wp_footer' ); ?>
2. Create Function For New Hook in Parent Theme
function create_after_footer_hook() {
do_action('after_wp_footer');
}
3. Add Hook In Custom Function Using Child Theme
function your_function_name() {
echo 'Replace this entire line of code with your code to do stuff';
}
add_action('after_wp_footer', 'your_function_name');