Kammala jumla mai zuwa: A lokacin zamansa biyu a Stanstead, Jankowski da sauri ya sami tsayi, yana girma zuwa 6'2" tsayi, yayin da wasansa ne ya ja hankalin 'yan leken asirin. Daga ƙarshe an zaɓe shi a cikin shirin OHL na 2012, wanda aka ɗauka a matsayin na 11 a zagaye na 7 na Saginaw Spirit duk da cewa ya ƙi shiga ƙungiyar. Ofishin Kula da 'Yan wasan Kwallon Kafar Kasa (NHL) ya sanya Jankowski a matsayin mafi kyawun fata na 43 don
2012 NHL Entry Draft a matsayinsa na karshe, ci gaba daga matsayinsa na 74 a cikin rahotannin da suka gabata. Sauran manazarta sun ba shi matsayi mafi girma, gami da Craig Button na Cibiyar Wasannin Wasanni, wanda ya sanya shi na 41. Calgary Flames sun zaɓe shi a zagaye na farko, na 21 gaba ɗaya. Shi ne wanda aka fi zaɓa daga makarantar sakandare ta Kanada. The Flames sun sami wasu zargi don fita "daga hukumar" da zaɓar Jankowski sama da inda aka sa ran zaɓa, amma mataimakin manajan Janar John Weisbrod ya bayyana cewa yayin da baiwar Jankowski ta kasance "tsabtace", sauran ƙungiyoyi sun tabbata za su zaɓe shi a zagaye na farko idan Flames ba su yi ba. Babban manajan Jay Feaster ya yi jayayya cewa Jankowski yana daya daga cikin 'yan wasan da suka fi kwarewa a cikin shirin. A lokacin da aka zaɓa shi 6'2.5", 168 fam.