For QxC cloud-connected gateways, there are no specific inbound ports which need to be open as all communication is initiated from the private side by the gateway. In the off chance your network blocks outbound ports, you will need to open the following: Outbound UDP port 51820.
If this is a QXOP on-premises gateway that you would like to access from outside your site's internal network, you will need to ensure that the router's public-side port 20824 is forwarded to port 443 on the gateway's private IP. Please refer to your router's manual for configuration assistance. (www.portforward.com is another good online reference)