Second one-shot prize is done!!! Wow that's actually the fastest I've ever written for a story O.O anyway the correct answer is that because the info about the dance exam was the last item in the email and J-Hope did not finish reading the email (this was the clue in chapter 17), he did not know about it. 

The request for the prize was of Taehyung and his birthday, which was on the 30th. Here is the fanfic: 

http://www.asianfanfics.com/story/view/885568/i-m-yours-fluff-you-birthday-bts-taehyung-btsv-taehyungxyou

Happy birthday to the amazing 4D alien~