Harvard University researcher Brian Friedberg operates like a detective, snooping in the dark recesses of the Internet. His main target is the far-right conspiracy theory QAnon, a shadowy movement described in a recent CNN report as “dangerous and growing.” Q has surfaced as a factor in congressional races and news coverage in the 2020 presidential election. “We are Q” posters and T-shirts have appeared at President Donald Trump’s rallies, sending up red flags. Operatives function a...