Here is my 100% Achievement Guide for Liquid Sunshine!
Located in chapter 6.
After the second checkpoint, is where we see and use elevators for the first time.
Press up to go up with both monkey and horse.
Throw monkey over by pressing
with the horse and there is another elevator there.
Simply go all the way up and you will see the next diamond.
Go to 33:00 to see this one
Hope This Helps!