What You Did
You demonstrated the presence of phosphors in both tonic water and highlighter fluid. Phosphors are luminescent, which means they can be either phosphorescent or fluorescent. Both the tonic water and the highlighter are fluorescent because they emit low energy visible light after absorbing the high energy UV light from your black light.
Both jars should glow under the black light.
If your black light doesn’t emit UV light, the liquids will not glow.
Leave a flower in the jar of highlighter water for 24 hours, then observe it with the black light.Gather up different rocks and observe them under the black light. Some minerals fluoresce too!