1 cup lemon-lime soda (such as Sprite®)
1 (3 ounce) package pineapple-flavored gelatin mix (such as Jell-O®)
3/4 cup peach schnapps
1/4 cup cold water
Heat soda in a medium-sized pot over medium heat until simmering. Pour in pineapple gelatin mix and stir until fully dissolved.
Remove mixture from heat and stir in peach schnapps and cold water. Cool to lukewarm, 5 to 10 minutes.
Pour mixture into 2-ounce cups and refrigerate until set, 3 to 4 hours.