Adding comments section to specific pages

Open page editor, press “Screen Options” and check “Discussion” -> scroll your page and allow comments http://prntscr.com/9wxwo8

If you want to add comments to Fullwidth template, firstly, you should edit code of this template. Go to menu Appearance -> Editor and find Page fullwidth Page Template (page-fullwidth.php)

Then copy & paste this code

                    // If comments are open or we have at least one comment, load up the comment template.
                    if (comments_open() || get_comments_number()) {
                        comments_template();
                    }

after this part of code

 // Start the Loop.
                while (have_posts()) : the_post();

                    the_content();

You must have next result

Now you can enable discussion in page editor via Screen Options.