On Pega 7.2.2, KM "Community" Link is contained in OOTB section "KMUpperHeaderSection" which is an extension point for the users to customize header of KM Help Site. The action for its click event is to launch OOTB Harness, "KMCommunitySitePortal". You can also launch your own Harness.
The OOTB header section is provided as a sample only. It is expected that during an implementation
customer can display the help site within an existing web self-service application and utilize an existing
Please refer below KM 7.22 implementation guide in "Configuring header bar" section (pg 37) for more detailed information.