Hi,
The order custom fields are displayed in the checkout thanks to the step called "fields".
If this step element is not in your checkout workflow, the order custom fields won't be displayed to your customer.
Please check your checkout workflow configuration for that element.
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.