Nickelodeon Kart Racers 2: Grand Prix

You're both right, one can use both the ramps and the half-pipes for this. And this achievement seems to unlock after the race ends so one should keep count. It would be helpful if you described what a jump boost looks like on screen.

It looks like anything else. The difference seems to be the flipping yellow ramps rather than static ones

I believe LB is to do a stunt and not required, for this you can just drive off ramps and half pipes and receive a boost upon landing with no stunt, that's how i got this.

LB at the top of a green ramp to do a Slime Stunt ALSO counts as a jump boost. If you don't hit one of the green ramps, but instead jump and fall the height of 3-4 carts and hit LB right before you land, you will perform an actual jump boost. If you don't activate the Slime Stunt at the top of the jump, you can always save it with the Jump Boost at the BOTTOM of the jump. You'll know you've done it right when you get a speed boost and slime flies out of your exhaust. You can't do both a Slime Stunt and a Jump Boost. Arena was the easiest place to do this.