Someone edited a question of mine. They made at least one bad edit, so I'd like to see what changes they actually made. How can I do that?
You can see the changes by looking at the revision history, which you can access by clicking the "edited X minutes ago" link (Example: the revision history for this question which I just edited). Once inside, you can use first three buttons on the left to switch between
The last button is a permalink to that revision.
Use the revisions page.
Once the question has been edited, the name and stats of the last user to edit it should show up next to those of the user who posted it. The text "edited [time] ago" is actually a link and will take you to the revisions page of the post.
For each revision you will see red highlights to mark content that was removed and green highlights for content that was added.
Clicking this button:
Will show the revision immediately preceding the one whose corresponding button was clicked next to it for closer comparison. @Yoda has an image of what that looks like.