Depending on your version of Windows, the folder where the offline tracks are synchronized can change a little bit.
However, on the latest versions, the folder is:
Program Data/Recisio/KaraFun 2/Cache
You need to change the default behavior of Windows in order to show hidden folders.
Warning: changing the structure of this folder might cause KaraFun Player to crash, and we can't ensure technical support if this folder is moved or changed.