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.
Also during the trip, the president criticized Amazon, the internet retail titan he has repeatedly attacked in recent days. He contended other retailers do not have a level playing field with Amazon and said it needs to change.
He noted that the Supreme Court is expected to decide later this year on whether all Amazon transactions will be subject to state sales tax.
"We'll see what happens," the president said.
Amid a string of damaging reports about Environmental Protection Agency Administrator Scott Pruitt, Trump said he is "doing a great job."
Pruitt has been mired in controversy over a deal to rent a condominium linked to an energy lobbyist last year. He has also faced backlash for his conduct and spending at the agency.
The White House was reportedly upset with Pruitt's combative Wednesday interview on Fox News.
The president also said he planned to send between 2,000 and 4,000 National Guard troops to the U.S. border with Mexico.
Trump did not know specifically how much it would cost to send the troops there.