I visited a Wikipedia page about cartoons created by the Chinese government, whose image I feel would fall under fair use.
Going through the article history, I see that there was a link to an image before at this address, but then the link broke, presumably because the image was removed due to copyright concern, and was removed from the article.
How can I see the discussion that contains the reason why that image was removed, so I can try to upload a valid image if possible?
Go to what would be the file page if the file existed, i.e. File:Chacha and Jingjing.jpg, and it will have a link to the deletion log. There you can see that it was deleted with "In category Media missing permission as of 10 January 2011; no permission". That is probably routine cleanup without discussion; that is, the uploader did not explain why this image is free to use, and the administrator did not have time to do their work instead of them. (Also, fair use images would have to be uploaded to English Wikipedia, not Wikimedia Commons, which is for free images only.)
In this case, the file was deleted, because it was missing permission, i.e. license. It is not necessary to have a discussion about delegation if the case is clear. Sometimes when files are deleted it's a result of a discussion, but not always. In this case, I am even not sure if the image was used on Wikipedia under fair use. I guess not, because it was not stored locally on en.wikipedia.org. While on English Wikipedia you can use images under the fair use principle, you cannot do that on Wikimedia Commons, where this file was physically stored.
