[5] During his two seasons in Stanstead, Jankowski quickly gained height, growing to 6'2" tall, while it was his play that caught the attention of scouts.

Jankowski initially committed to play for the Dubuque Fighting Saints of the United States Hockey League (USHL) in 2012–13 before for Providence.

[4] However, he decided to bypass the junior league and move directly to college following the Flames' 2012 rookie development camp, stating he believed he was ready despite the fact that he will be one of the youngest players in the National Collegiate Athletic Association (NCAA).

The deal began during the 2016–17 NHL season; for the remainder of 2015–16, Jankowski played with the Flames' American Hockey League affiliate, the Stockton Heat.

[14] After a largely disappointing 2019–20 season, in which Jankowski was limited to a fourth-line role and contributed with just 5 goals and 7 points in 56 games, he was released by the Flames as a free agent after he was not tendered a qualifying offer to retain his rights on October 8, 2020.

On October 15, 2021, he agreed to begin the 2021–22 season with the Rochester Americans of the AHL, signing a one-year deal with the primary affiliate of the Buffalo Sabres.

[18] After collecting 5 goals and 12 points through his first 13 games with the Americans, Jankowski was signed to a one-year, $750,000 contract, with the Buffalo Sabres on November 28, 2021.

[1] His grandfather, Lou, was a longtime professional player who appeared in 127 NHL games with the Detroit Red Wings and Chicago Blackhawks in the 1950s.