Qlik Sense uses ports for communication between web browsers (users) and proxies, and between services in both single-node and multi-node deployments.
The product comes shipped with the Qlik Sense Utility, which includes a Port Checker. See Qlik Sense Utility - Functions and Features.
Please see Ports Overview in Qlik Help for more details on what ports are used by the Qlik Sense services. Remember to select the accurate product version in the help page in order to obtain accurate port information.