How to show show the Second page title in the page

get_post_ancestors() returns all of the ancestors hierarchically. As you only want to display the 2nd level post title on 4th post page, you can do something like –

global $post;

$parents = get_post_ancestors( get_the_ID() );

if( count($parents) == 4 ){

    // ancestor1 = 1st parent, ancestor2 = second.
    echo get_the_title($parents['1']); // index starts from 0, 1 = 2nd item
}