The best place in Noki Bay to collect 100 Coins is on Episode 6: The Shell’s Secret due to the appearance of many coin trails along the water where you start.
From your starting position, turn around and drop into the water, using the Hover Nozzle and constant presses of the A button, follow the long Coin trail until you reach the bank on the otherside, there’s a total of 50 Coins to collect in this section alone (50). Head right from here and then look to the cliff and spray the square to cause a pathway to appear and follow the right path to the top.
Run across to the left and then leap down to an alcove with a square switch on it again. Spray with the FLUDD to cause a new path to appear and then Wall Kick up the walls here and enter the alcove on the left, second highest. Follow the path here to collect another 13 Coins (63) before exiting from the other side and then return to the platform with the switch, spraying it again to cause the hidden paths to appear once more.
This time, enter the first entrance below and to the left and follow the path to collect another 11 Coins (84). Follow the path from the exit up and to the left, shooting you to the top where one more coin can be found on top of the tree (85). Finally, make your way back down to the platform with the switch one final time, activate it and enter the top right entrance to find the final set of Coins (100).
The Shine will appear on top of one of the large shells in the center, make use of the ropes, avoid the Traps and once you reach the very top, claim your prize.