Alek Skarlatos, an Oregon Army National Guard specialist who came to world attention when he helped thwart a gunman on an Amsterdam-Paris train this past summer, has since placed as a finalist on “Dancing With the Stars.” Skarlatos and partner Lindsay Arnold are among the couples appearing tonight live at the Beacon Theatre, 2124 Broadway at 74th St. Jan. 6, 8 p.m. Tickets are $49.50 – $79.50 at beacontheatre.com.