no fortune with that in NickelMenu
Code:
menu_item :main :Import books :nickel_misc :rescan_books_full
I gave up and create another folder on my Kobo Clara BW where i transfered the books from Calibre WiFi connection and they are now recognized in Calibre as expected.
Synchthing is usless in my case, i just use Calibre to send books to the Kobo folder (/mnt/onboard/koreader/)