EDIT: This is in Chain of Memories
This minigame is located in the 100 acre woods, which becomes available after clearing the floor 6 of Castle Oblivian. There are no enemies or combat here but instead a series of minigames, with Tigger's Jump-a-Thon being the third.
The minigame is just a memory game with Tigger jumping between 4 stumps labeled with
and you get one point for each correct jump.
I recommend getting a pen and paper or using the note pad on your phone to write down the sequence because it gets fairly long before reaching the required amount of points. The sequences don't change each time instead, building on the same sequence and making it longer so it shouldn't be to hard write down.
After obtaining the 120 points you have to lose the minigame before the achievement will pop.