Problem:
I need to add a comment system in each product, which plugin can I use or in what way I could incorporate it?

Solution:
To enable WordPress Comments for Custom Post Type you can follow the steps mentioned here: https://toolset.com/forums/topic/how-to-add-comments-to-custom-post-type/

If still there is a problem, first you need to check if WordPress comments settings are correct or not. Please see attached screenshot for default WP Comments settings, you need to make your settings same as in my screenshot:
https://cdn.toolset.com/wp-content/uploads/2018/07/954639-WP_Comments_Settings.png?x28969

-- To change these settings go to: WP Dashboard >> Settings >> Discussion tab >> change the settings and Save Changes, and then check if it resolves the issue.

-- Also in the video you are looking inside Layout template for the Discussion / Comments section. You actually need to go to Listings post type >> click on Product 1 or Product 2 >> there you will find the Discussion / Comments sections to allow the comments.