Getting an error while getting in ringcentral extension.......You cannot use this device to make PSTN calls including Emergency Calls since no Digital Line is associated.

Tell me more about what you did. What environment, sandbox or production. And the exact steps that took you there.

The message said that you don't have a digital line associated with the user extension. Can you login the service web, select the user -> User Details -> Phone to see if the user has a device or not. If not, click the "Add Phone" button to add a digital line to that user extension and try again.

this option is not coming for RingCentral Video Pro user, do we need any specific licence for this 

Yes, Video Pro user is a free license and such a user cannot have a DL. You need a RingEX license available to add a phone to that user, then the user will become a RingEX user.