How to sign up for Jedi Training:
NOTE: As of recently, DHS has been actually opening to guests (unannounced) at some time between 8:30 and 8:45AM (or so) on days when the published opening time is 9AM.
Don't know if this will be the new "norm," but I'd plan on arriving at DHS -at least- by 8:15 so as to be in a better position to sign up for Jedi Training and to grab TSM FP's.
On AM EMH days, I'd be there much earlier (if you are a WDW Resort guest)
as they have been signing kids at some point before regular opening time on EMH days.
So... arrive well before park opening time.
When you get inside, take the child with you to the sign-up area.**
You'll get a time for the child to return to the Jedi stage and participate.
**Sign-ups will be either just past Hollywood & Vine Restaurant, or at the Sounds Dangerous entrance
(on some days, even inside Sounds Dangerous building,) or at the Jedi Stage.
Look for the sign-up area, in the order of the above, until you find it.