OP's headline does not match the article linked in any way. I don't know if the site changed the article or what, but the Grand Jury has not ordered Reddit to turn over any data.
a subpoena issued by federal prosecutors to the management of Reddit, representatives of the site have been ordered to appear before a grand jury in Washington D.C., with an April 14 deadline set in an attempt to compel Reddit to volunteer personal data and the identity of a user who had the temerity to lightly criticize Immigration and Customs Enforcement (ICE) on the platform.
Essentially, they have ordered Reddit to send representatives to be badgered into volunteering the user's information.