Is a notification sent to someone who downvoted a question when that question has been updated?
Initially, my question got a downvote because it was lacking sufficient information/code/explanation/etc..
Now, I have updated my question & it looks good. Will a notification be sent to the downvoter that this question has been updated, so that the downvoter can review the question again & if it looks good to him/her they can remove the downvote?
No, it does not. It is entirely to a user to revisit his/her votes if they are still valid. Users vote on a post as-is and there is no requirement to visit a post again to review it again.
If a user really cares, he could check the favorite star next to the question. He will receive updates through his user profile. I don't think there are much users doing that. It is just so much work to go over your downvoted questions again and again.
The question will get bumped to the front page, so it should get eyes and possibly votes that correct the post score.
The lesson you should learn: try to make it right the first time. I know it is hard, but if you learn how to review your post before submitting, you have a much better chance of it being well-received.
No. Voters are not notified when your post is edited.
If you are going to notify downvoters then you need to do the opposite too, it's completely possible to edit a good question to a worse state and that deserves just as much attention.
I vote quite a lot and I honestly don't want to be notified when every post I have ever voted on is edited. Lots of posts get edited, some a long time after being voted on.
Your post is bumped to the top of the feed when it is edited so it is already getting fresh eyes. If it really has improved, you will get upvotes to counter the downvotes, hopefully some of the downvoters will see the question has improved and reverse their vote. Other than that, the answer really is to not post unclear questions to begin with.
