Dorsey, who stepped down from the CEO role last year and left the board in May this year, had announced his support for Musk's $US44 billion ($A64 billion) acquisition of Twitter in April.
According to a filing with the US Securities and Exchange Commission, the subpoena seeks documents and communications from Dorsey about the Twitter buyout agreement, reports said.
Dorsey was also asked about spam and fake accounts and its impact on the platform as well as Twitter's use of monetisable daily active usage (mDAU) as a key metric.
The subpoena was filed as Musk is preparing to face a five-day trial in a lawsuit from Twitter on October 17 in the Delaware Court of Chancery over his intended termination of the planned acquisition of the social media.
Judge Kathaleen McCormick earlier had ordered Twitter to collect, review and produce documents from Kayvon Beykpour, who was the general manager of its consumer product division.
Meanwhile, Musk's legal team is seeking information from Bruce Falck, who previously lead Twitter's revenue product division. It was in late April that Twitter agreed to accept Musk's offer for $US54.20 ($A78.93) per share in cash and to become a privately held company.
Dorsey had tweeted in April that Musk was the singular solution he trusts to run Twitter, and that both Musk and Twitter CEO Parag Agrawal's goal was to create a platform that is maximally trusted and broadly inclusive.
