You probably don’t need a recipe.
Ask him exactly what he remembers being in it, then wing it. Be sure to ask what he thought the base flavor of the jello was and how big the pieces of vegetable were.
You’ll probably have to make it a few times, asking him for guidance, before you get close to the one he remembers, but it would probably be a fun venture.
These jello salads were colorful, a combo of textures and every family had their own version.
In my family it was a red jello, I think it was raspberry but could have been strawberrie, and it had fruits and sour cream in it. I especially remember the grapes, they’d always be cut in half.