Hello,
Unfortunately, you won't find any setting to do that directly.
You need to perform some modifications/customization.
An account (Joomla and HikaShop) can have only one single email.
You can see to use "user custom field" to store extra data but in such case you would need to override your customer email preload to handle that specific value and add the extra addresses in CC.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.