The demo will be titled, Final Fantasy XV:Judgment Disc. This was announced by Final Fantasy XV’s Twitter account.
無料体験版『FINAL FANTASY XV JUDGMENT DISC』明日11日(金)に、PS Store / Xboxストアにて配信決定！！！日本国内限定配信の特別体験版で、オープニングからエピソード１の途中まで遊べます！ #FF15 #FFXV pic.twitter.com/ilj9BfE1PR
— FINAL FANTASY XV (@FFXVJP) November 10, 2016
In the demo you play the opening of the story. Though you cannot carry your data over to the full game. The demo will span to the middle of chapter 1.
You can grab the demo tomorrow on the Japanese PlayStation Store.