Contextual Shared comments on nodes that are clones of one another
There's many routes which to take for this. Drupal 8 gives you a bit more flexibility than previous versions. For the sake of managing a shared comment section, you can go about creating a new body-less content type that only contains: 


A comment field
A node reference field with 2 entries (one for the parent &amp; child cloned node)


Upon your clone operation, you can create a new entity with a dummy, to-be-hidden, title and the node reference field populated with the parent/child nodes.

For display/commenting, you can create a block view that uses a Provide default value: Raw value from url (Path component: 2) (i.e. the node id) contextual filter so the block only displays the shared comment entity on viewing the child/parent nodes.