1. Pour the cold water into a small bowl. Sprinkle the packet of Knox gelatin evenly over the water. Let it stand for 1 to 2 minutes to soften and bloom.
2. In a small saucepan, heat the fruit juice over medium heat until it is hot but not boiling. If using sugar or honey, stir it into the hot juice until fully dissolved.
3. Remove the hot juice from the heat. Add the bloomed gelatin mixture to the hot juice and stir continuously for about 2 to 3 minutes, until the gelatin is completely dissolved.
4. Pour the liquid gelatin mixture into a serving dish, a mold, or individual cups. If desired, add small pieces of fresh fruit to the mixture before it sets.
5. Carefully place the dish in the refrigerator. Allow the gelatin to chill and set completely, which will take at least 4 hours, preferably overnight.
6. Once fully set, the gelatin is ready to serve. To unmold, dip the bottom of the mold in warm water for a few seconds, then invert onto a plate.