At the End of Chapter 2, Tim and Pikachu will Find a broken Vial found within the Apartment that use to belong to Harry Goodman, Tim's father that suddenly disappeared two months ago. After finding said vial, Tim and Pikachu will learn of a laboratory in Ryme City from Mr. Baker called the PCL. The following day, with the beginning of Chapter 3, Tim and Pikachu will go undercover as the newest employee of the PCL.
While at the PCL, you will need to gather both Clues and Eyewitness Testimony in order to proceed through the PCL Buildings. While investigating, you will learn that Klefki is the only one with keys to the Storage Room in Building B. In order for you to get it to open the door to said room, you will first need to obtain some Shuckle Juice from Shuckle itself within the PCL Courtyard. Before being able to obtain said juice for Klefki, you will need to help Nina, one of the researchers at the PCL, complete her experiment with Shuckle.
In order to help Nina complete her experiment, you will need to gather berries from the trees in the courtyard and various liquids from around the PCL. After obtaining all of this, you will need to return to Nina and give her the proper ingredients so the experiment can be completed. By mixing a Red and Yellow Berry and then giving this new orange Substance with the Liquid Solution you received from Wallace straight to Nina, you will easily complete her experiment.
Once the experiment is complete, Shuckle will give you some of its juice. After handing it over to Klefki, it will unlock the door to the Storage Room found in Building B of the PCL. By investigating this room, Tim and Pikachu will Find a Vial that will match that of the broken one found back at Harry's Apartment.