Hi @simonb20487028
you can apply for access to a CJA sandbox here: https://business.adobe.com/resources/customer-journey-analytics-sandbox.html
Note though, that unfortunately, this merely gives you access to preconfigured dummy data views, but won't give you any admin access to configure Connections nor Data Views. So, you can practically only play around with the new visualizations, but not use derived fields or similar that require admin access.
This is a limitation that many of us who would be interested in deepening their experience with CJA are facing (maybe someone from Adobe reads this).
I have flagged this many times, unfortunately without success.
Cheers from Switzerland!