You are no longer able to find the magical quill, as the challenge has ended. You had to answer the question correctly in order to find the quill.
The aim is that you must find your way to pottermore. On that site you will find the magic quill, clicking that will let you register.
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Each day a new clue was released which, if answered correctly, led to one of Pottermore's partner websites. The quill would be hidden somewhere on the main page of that website.
You have to wait until it opens in October.
The clues were on the Pottermore website in the middle of the page. They appeared at different times throughout the seven days.
August 5, 2011
August 4, 2011
August 2nd 2011.
There was no separate website for Pottermore beta testing. To access it you had to successfully complete the Magic Quill Challenge. The site is now open to all.
The quill was located on the registration page. On day 4 of the challenge, an error meant users were redirected straight to the Sony site instead of searching for the quill. This was fixed after a few minutes.
The clue on day 2 was released at 9am GMT.
They were released at different times everyday to allow for different schedules and timezones.