Thank you for your explanation.
I have found the .onyx directory. The point is that it doesn't contain any *.sketch file.
It contains just one file:
[19:05:19 .onyx]$ ls -la
drwxr-xr-x 2 32768 jan11 12:41 .
drwxr-xr-x 3 32768 jan 10 08:42 ..
-rw-r--r-- 1 35840 jan 11 12:41 .thumbs.db
Moreover, even if it is a "SQLite format 3" file, it has not been updated today, yet I just added some bookmarks to a file in the parent directory a few minutes ago.
Also, if I perform a "find . -cmin -60" in both directories regarding internal/sd memory, no file is found.