Please follow the steps below: 

1.Put the following code in the active theme functions.php file:

function my_wpdiscuz_shortcode() {
    $html = "";
    if (file_exists(ABSPATH . "wp-content/plugins/wpdiscuz/themes/default/comment-form.php")) {
        ob_start();
        include ABSPATH . "wp-content/plugins/wpdiscuz/themes/default/comment-form.php";
        $html = ob_get_clean();
    }
    return $html;
}
add_shortcode("wpdiscuz_comments", "my_wpdiscuz_shortcode");

2. Drag and drop the "Shortcode" element from the Elementor widget panel onto the page. Insert this shortcode: 

3. Enable the comment form for the current post type. 

That is: the shortcode can be used if the post type supports comments.  

I'm using Elementor "free" version and "shortcode" widget to show comments on blog post.

Please let me know what value should I use for "shortcode" ?

Thanks in advance.

I'm following below instructions for elementor page builder

1. Once the plugin is installed and activated, go to your Elementor editor and navigate to the page where you want to add the comments section.
2. Drag and drop the “Shortcode” element from the Elementor widget panel onto the page.
3. In the shortcode element, enter the shortcode provided by the comments plugin.