Not registered with IANA and not tied to any well-known service — whatever answers here is site-specific.
6896 has no entry in the IANA service name and port number registry, in either transport. Nmap's services file lists it as "unknown" with an open-frequency of 0.000152, which puts it among the ports it almost never sees open in internet-wide scans. There is no established software, protocol, or malware family that claims it. If it is listening on your host, the answer comes from the process table, not from a port list.
Expose with care
An unregistered port tells you nothing about its risk; identify the owning process with lsof or ss before deciding whether it should be reachable.
$ sudo lsof -nP -iTCP:6896 -sTCP:LISTENSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.