Add a Page Template column to the WordPress admin "Pages" page

page-template-column.php

<?php

/**
 * Introduces a new column to the 'Page' dashboard that will be used to render the page template
 * for the given page.
 *
 * @param array $page_columns The array of columns rendering page meta data.
 *
 * @return array $page_columns The update array of page columns.
 */
add_filter('manage_edit-page_columns', function ($page_columns) {
    $page_columns['template'] = 'Page Template';
    return $page_columns;
});

/**
 * Renders the name of the template applied to the current page. Will use 'Default' if no
 * template is used, but will use the friendly name of the template if one is applied.
 *
 * @param   string $column_name The name of the column being rendered.
 */
add_action('manage_page_posts_custom_column', function ($column_name) {
    // If we're not looking at the 'Template' column, then we're done.
    if ('template' !== $column_name) {
        return;
    }

    // Grab a reference to the post that's currently being rendered.
    global $post;

    // First, the get name of the template.
    $template_name = get_page_template_slug($post->ID);
    $template      = untrailingslashit(get_stylesheet_directory()) . '/' . $template_name;

    /**
     * If the file name is empty or the template file doesn't exist (because, say,
     * meta data is left from a previous theme).
     * Otherwise, let's actually get the friendly name of the file rather than the name of the file itself
     * by using the WordPress `get_file_description` function
     */
    $template_name = ( 0 === strlen(trim($template_name)) || ! file_exists($template) ) ? 'Default' : get_file_description($template);

    // Finally, render the template name.
    echo esc_html($template_name);
});