Unfortunately Jooki is no longer available for sale.
There is a Jooki community on Reddit where owners help each other: https://www.reddit.com/r/jooki/
An archive of the Jooki firmware source is available at https://jooki.com/jooki-archive-20261026.tgz
The Muuselabs-authored portions of the Jooki firmware source are released under the MIT license. The archive also contains third-party components under their own licenses (including GPL, LGPL, BSD, and Apache), which are not covered by this grant. If you use this code you are responsible for determining and complying with the applicable licenses.