Trump spoke to reporters for the first time about the payment, made shortly before the 2016 election, to secure Daniels' silence about allegations of a sexual encounter with the president years ago. Representatives for the president have denied that Trump and Daniels engaged in a tryst.
The president said Thursday he did not know where his personal attorney Michael Cohen got the money.
During an Air Force One trip back from an event in West Virginia, he told reporters they would have to ask Cohen about why the lawyer made the payment. Cohen has said the money came from his own pocket.
Cohen's action has prompted questions about possible campaign finance law violations.
Last month, Daniels, whose real name is Stephanie Clifford, sued Cohen to try to get released from a nondisclosure agreement she signed in October 2016.