From the New York Times:
"Of the three Americans currently known to be held in North Korea, two were arrested after Mr. Trump took office — meaning the Obama administration would not have sought their release.
Kim Hak-song was arrested on May 6, 2017. He worked at Pyongyang University of Science and Technology, a university founded by American evangelical scholars.
Tony Kim, also known as Kim Sang-duk, was detained on April 22, 2017. He taught at the same university in Pyongyang for a month."