Thank's a lot CST and Frenzie for your quick responses!
The problem is that on my computer "/mnt/onboard/" is displayed as the root directory (I can't see the "mnt" and the "onboard" folder.
And at the opposite, I can't find the ".add" folder on Koreader because it's a hidden folder.,
I have copied the files to root directory and set the Zotero Path to mnt/onboard/ and is has find the directory
!
I have now an other porblem, When I Browse my Zotero collection under Search > Zotero > Browse Database, it doesn't work and it shows an error message (see photo). Can someone help me again. Thanx a lot and have a nice day