Page title not showing up

to show the page title for the page set as the ‘blog’ or ‘posts page’, you need to add some code, maybe via a filter on wp_title();

example:

add_filter( 'wp_title', 'wpse_174379_show_posts_page_wp_title' );
function wpse_174379_show_posts_page_wp_title( $title ) {
    if( get_option( 'page_for_posts' ) ) { 
        $posts_page = get_post( get_option( 'page_for_posts') ); 
        $title=" " . $posts_page->post_title . ' ';
    }
    return $title;
}