Currently, the achievement popup displays the net reputation delta derived from posts grouped by question title, eg
+25 Some question title
+10 Some other question title
+20 Some old question title
As well as the delta, it would be good to show the post's current vote breakdown, eg
+25 (✓1/0) Some question title
+10 (2/5) Some other question title
+20 (24/0) Some old question title
(The tick means "accepted')
Note the second example: Without the extra info, we will likely think we got 1 upvote and leave it at that, but actually we got 2 up and 5 down votes and so should investigate the apparent problem with the post.
Interest (to avoid score curiosity click through):
You notice you're got quite a few votes for a post and are curious as to its score, but to find that out you have to open the question (and you only want to see the score and nothing else). With the extra info, you don't need to click through - you can see you're 1 upvote away from a "Good answer"
The edge case of someone answering their own question could be handled by splitting into two vote summaries, perhaps:
+15 (Q:3/0 A:5/1) Some self-answered question title
The exact format of the vote data would likely be the subject of a UX debate. This question is more about whether it the vote data should be shown or not - not so much how to show it, although ideas are welcome.