To use Chilkat for signing XML with a CNS smartcard, the certificate must be installed on the Windows system. Chilkat uses the Microsoft CNG (Cryptographic Next Generation) to do the signing. If the CNS smartcard certificate is installed on Windows correctly, then CNG should automatically know to use the smartcard for signing. I cannot read Italian, but I think the instructions for installing on Windows can be found at one of these URLs:
https://www.card.infocamere.it/infocard/pub/guide-installazione_5390
http://www.progettocns.it/common/kitcittadino.aspx