Line a 23 x 13-cm (9 x 5-inch) pan with lightly oiled plastic wrap.
In a bowl, sprinkle the gelatin over 180 ml (3/4 cup) of juice and let stand for 1 minute.
In a saucepan, bring the remaining juice and sugar to a boil and cook until the sugar has dissolved. Add the gelatin mixture. Bring to a boil over medium heat and cook for 2 minutes. Skim. Pour into the prepared pan and let cool. Refrigerate for 8 hours.
Remove the pan from the refrigerator and allow to come to room temperature for 3 hours. Unmould and cut into 2.5-cm (1-inch) cubes.
In a bowl, combine the sugar and cornstarch.
Roll a few jujubes at a time in the sugar mixture and shake to remove any excess.