I don't think there is a single piece of knowlege that needs to be known by everyone, if it did it would already be known. In fact it's far more likely that there is no knowledge that should be known by everyone. It is not one of the fundamental properties of truth/knowledge that it is always good for someone/anyone to know it, and we should be more cautious about this in general I think. But this too, is not something everyone should know.