It's a tribute event held at SMTOWN theatre of December 17th. They're asking fans and people touched by Jonghyun's passing to take part in a few different ways.
what a touching tribute and event for fans. looks like it's open to anyone wanting to submit! A link to register for the site (it's in korean but there should be fan translations on what to do soon) > https://www.shiny.or.kr/login?back_url=LzQyLz9pZHg9MTM4MjI1MiZibW9kZT12aWV3&used_login_btn=Y