If you "just" want to see the post edit history of a post, check "Steem Scribe" here: https://scribe.steemian.info/
The infrastructure behind this service is described here: https://steemit.com/steem/@drakos/steem-scribe-posts-and-comments-history
If you're interested on how to retrieve this information from the blockchain yourself: Parse the account history of the author for any `comment` operation with the given permlink. Edits can either be in a "diff" format, replacing parts of the previous version, or full replacements of the posts.