Hi Lexi,
This is a good question; I can tell you that there are two main ways to do this.
1. Using the top tool bar, click Edit and this will drop down a list of options. If you then select Function Explorer you will be taken to a Library of the Functions used by KnowledgeKube.
I have attached a couple screen shots to help guide you.
2. There is also a short cut option when in an Expression Editor panel for opening up a list of not only functions but keywords that are available for use with the loaded Model (Intellisense).
To Access this use the keyboard shortcut CTRL + Space.
Some other quick shortcuts that I find helpful are:
ALT + Left Arrow - Actions
ALT + Right Arrow - Forms
Alt + Down Arrow - Data Sources and Filters