I don't know the power dynamics of the company where @DarkCygnus works, but in the absence of an explanation as to why other people are Cc'd into a conversation, it would seem rude to me to Cc someone and then expect them to keep mute.
I will often start an email by saying something like:
I've Cc'd this to Bob, Charlie, and Dan, who are better qualified than me to investigate this issue.
Or in less cordial circumstances:
[this is Cc'ed to Yve (my manager) and Zak (HR) so that my responses are on the record]
So I would take an unannounced Cc as an invitation to participate if I am able to provide a meaningful contribution.
If I am Bcc'ed (and not behind a listserv), then that's different: perhaps they don't want the principal recipient to know that I'm receiving it, so I should tread carefully.
I concur with the earlier responders that being Cc'd generally implies you are not obligated to respond, and to avoid responding with vacuous one-liners when you're only Cc'ed. But if you're really in doubt you can simply reply-to-sender and ask.
Lastly, phrases like "does anyone know X", "do you know X", or "who knows X" are English language boilerplate, not to be taken literally; you should not answer "no" unless you are the only recipient of such an inquiry or the inquirer says they need replies from everyone.