There is no US law licensing journalists or people who report the news, or requiring such people to identify themselves by legal name. Nor can there be under the US First Amendment. There is also no law requiring a person to identify himself or herself by legal name online. Some sites, including Wikipedia, have policies against having multiple undisclosed user IDs for the same person, but that is a matter of the site's own rules, not a matter of law. Any US law mandating this would again run afoul of the First Amendment to the US Federal Constitution.
This article on Anonymous Speech reviews and cites a number of US Supreme court cases on the subject of anonymity, mostly in political contexts. This article from the Electronic Frontier Foundation (EFF) discusses the same general subject. Both articles mention that The Federalist (analyzing and advocating for the then-unratified US Constitution) was originally published under the pseudonym "Publis".
The EFF Article "Court Recognizes First Amendment Right to Anonymity Even After Speakers Lose Lawsuits" discusses the 6th Circuit case of Signature Management Team, LLC v. John Doe in which it was held that an anonymous blogger who lost a copyright infringement suit could nonetheless remain anonymous. This page apparently from a Harvard course, lists and briefly describes several cases on the same subject.
In Doe v. Cahill, 884 A.2d 451 (Del. 2005) an elected official sued an online poster for defamation, and sought to force the ISP involved to disclose the poster's identity. The Delaware Supreme Court ruled against this, setting a standard offering greater protection for such anonymous online speech than previous cases had.
This answer is very US-centric. Laws in other countries are different. The OP has not specified a country or jurisdiction.