Demo licenses are usually not directly available to individuals, but if you happen to have access to it, it's through our Tech Support channel. If you are associated with a company that has access to our products, talk to the account manager responsible for you. He may help you with license access.
Good to know that you are loving it!
Thanks for your interest in the PI System. There are some downloads that are free, such as the PI Developer Technologies for application developers. Even though that would be free, you would still require a data access license to a PI Data Archive. Usually this license can come from your company, but I see no company info associated with your PI Square account. What I would suggest is a PI Developers Club license, typically around 1500 USD per year. That would give you access to a PI Data Archive and AF Server - but not ProcessBook (very old) nor PI Vision (modern trending product).
Another option if you want to get hands-on with a sandbox PI System to practice building displays and more is to leverage OSIsoft's Virtual Learning Environment (VLE). You can learn more about the Virtual Learning Environment here. There are several options: One Month VLE Pass (currently $99), One Year VLE Pass, and specific VLEs that are designed for specific Online Learning courses.