In JS ? I know of one exemple of a double pop in rebound a few weeks ago, a young, very tall player with a super trainer and benefitting from a huge elastic effect. All conditions were perfect. It's extremely hard to achieve and it was the first and only time we have seen evidence of a double pop in the forum.
Now is it possible in JS ? JS trains fairly quick in double position but not as much as rebound in single for a tall player. I can be wrong, if someone did it I'd like to know :)