Right now, with the "new comment on facebook / instagram" triggers, we only get access to the comment body as a custom field to use in the workflow as {{fb_comment_on_post.fb.body}} and {{ig_comment_on_post.ig.body}}.
When we go to the contact, in the middle panel, we can see that there is a link to "go to post" which has the URL of the post they commented on - however there is no way to get this URL into a workflow at all currently, even though it is clearly in the data that GHL receives from the Meta API (see screenshot)
Additionally, when a user replies to another comment on a post, there is no way of getting any information about the comment that the user replied to (the parent comment). From what I see, it is possible for the parent comment to be pulled in via the API whenever a new comment is made.
This increased functionality will help make GHL a more useful tool for interacting with these platforms - this simple feature addition will bring so much increased functionality.