Collective intelligence is a form of wisdom of crowds. What together an aggregation knows is often pretty comparable with expert opinions. What is one word (or at most two) that describes this kind of community knowledge?
You're very close; Wikipedia says the preferred term is collective wisdom:
Collective wisdom, also called group wisdom and co-intelligence, is shared knowledge arrived at by individuals and groups.
This rather cuts across a classification I like:
knowledge: knowing what (ie basic factual knowledge)
understanding: understanding why (things inter-relate, work, happen)
wisdom: understanding how (to alter things for the better, and putting these changes into effect).
I believe you are looking for lore.
collective knowledge or wisdom on a particular subject, esp of a traditional nature
Crowdsourcing or 'Crowd sourcing' is today's common usage, and is so recognized for solving crimes/mysteries that public officials are directly appealing to enthusiasts
"Simply defined, crowdsourcing represents the act of a company or institution taking a function once performed by employees and outsourcing it to an undefined (and generally large) network of people in the form of an open call. This can take the form of peer-production (when the job is performed collaboratively), but is also often undertaken by sole individuals. The crucial prerequisite is the use of the open call format and the large network of potential laborers." -
folk wisdom: knowledge or beliefs associated with or traditional to the common people of a country