The following Facebook Graph API v2.6 query:
/{{POST_ID}}/?fields=comments.summary(true)&access_token={{ACCESS_TOKEN}}
will get the comments (with theirs IDs) for the specified Post. Then the query
/{{COMMENT_ID}}/?fields=comments.summary(true)&access_token={{ACCESS_TOKEN}}
will get the replies for the specified Comment.
Is there a way to get both the comments and their replies for given Post with one Graph API query?
This will get u the comment replies of comments.
You can get any sub info(from,id) of comment replies by just nesting fields inside comments like this:
You can always try out any kind of query at :
https://developers.facebook.com/tools/explorer/
In case you have any doubt on how to form any query, this tool has a search filter on left in which you enter the fields you require and it will automatilcally generate the query for you.