Career
Järnkrok was drafted 51st overall by the Detroit Red Wings of the National Hockey League (National Hockey League) in the 2010 National Hockey League Entry Draft. After a strong second half to the 2009-2010 season where Järnkrok got a regular roster spot on Brynäs, Järnkrok went from 21st among European Skaters in the midterm rankings to fourth among European Skaters in the Central Scouting final rankings for the 2010 National Hockey League Entry Draft. He was drafted in the second round of the 2010 draft by the Detroit Red Wings.
On March 5, 2014, Järnkrok was traded to the Nashville Predators, along with Patrick Eaves, as part of a deal that brought David Legwand to Detroit.
He was assigned to the Predators AHL affiliate, the Milwaukee Admirals. Järnkrok recorded an assist in his National Hockey League debut on March 21, 2014.
Järnkrok scored his first National Hockey League goal on March 27, 2014, against Matt Hackett of the Buffalo Sabres. During the 2014-2015 season, in his first full National Hockey League season, he recorded seven goals, and 11 assists in 74 games.
Järnkrok posted two goals and seven assists in his first 12 National Hockey League games, including five points in the first five contests of his National Hockey League career, the second-longest point streak by a Predators player in the first games of their National Hockey League career, behind Marek Židlický six games from October 9-23, 2003.
On July 17, 2015, the Predators re-signed Järnkrok to a one-year contract.