Get page ID of page that is set as the posts page

In WordPress settings you can set a page as the Posts Page. This can be found:

WP-Admin->Settings->Reading Settings->Front page displays

Front page displays settings

How do I retrieve the page ID that is set in this setting?

1

Use the page_for_posts option:

<?php
$page_for_posts = get_option( 'page_for_posts' );
?>

This will return the ID of the Page assigned to display the Blog Posts Index.