Jello, and most other products containing actual gelatin (which is what is in Jello) is neither vegan, nor vegetarian. It is made of the connective tissue of animals, the leftover parts from the slaughtering process, rather than the meat.
There are vegan “gelatin” options that are very tasty. You can read about that here: https://www.peta.org/living/food/vegan-gelatin/
I have tried the Simply Delish brand and it is very good.