As I previously noted,
While an approved edit can simply be checked in any post's edit history, the only ways to check rejected edits are either checking the suggester's suggestion history or one's own review history if one happened to review said edit.
As Gilles stated here,
in the mod menu under the post, select “show review history”. A review on a suggested edit on a post counts as a review on the post even if the suggested edit is rejected. This is a fairly recent feature, I think it was introduced in 2013 with little publicity.
i.e. there already exists a tool to show not only approved edits but also refused ones. And at least for one's own posts it would be adequate being able to re-view (or even re-review) them to make sure e.g. a "too radical" suggestion wasn't actually fixing a more or less severe oversight. edit2 Though there's probably no reason why this shouldn't be available for just anyone.
edit As Gilles said, the tool actually also shows all other review history items like low quality etc. I'm only requesting access to the suggested edit history. (Although as long as the rest doesn't expose too much user information it'd probably be less implementation work to use the tool as-is but only make it available on own posts unless one is a mod.)