We have two network interfaces on different subnets on a single machine
Now I have only one name server register it point to only one ip address on nic1
Now if I add another nic wirh different ip and mask point to same nameserver it will work directly ? Or I should register it ip ?

Yes ! You can ! Your provider must give you one more ip address!

Assuming that your name server uses Dynamic DNS and the second NIC is setup to register itself into DNS, then yes, it will.