Born in 1996, he grew up in the youth academy of Slavia Prague, a team from his hometown, before moving to Udinese in Italy at only 18 years of age. With the Friulani he showed his qualities already in the Primavera championship; on loan to Ascoli the following year, in his first season in the professional ranks, he stood out with 5 goals and 9 assists in 35 matches. He then returned to Udine to carve out a starring role for himself: in two seasons he played 69 matches, scoring 11 goals and 10 assists. In the summer of 2018, he moved to Sampdoria, where he will be coached by Claudio Ranieri from October 2019: perfectly integrated in the coach's schemes, with him on the bench he will be able to get the best satisfactions in the blucerchiata jersey, where he will collect a total of 97 appearances with 9 goals and as many assists.

In August 2021, he moved to La Liga in Getafe; he played last season in his homeland with Sparta Prague (16 matches and 1 goal), with whom he won the Czech Republic championship title.

He currently boasts 45 appearances, four goals and 11 assists with the senior national team.

Jankto is a particularly ductile left-footed midfielder, who can be used both as an inside player and as a flanker. With his tactical intelligence, he knows how to find the timing to get into spaces; his disruptive running allows him to make his way up the wing to serve inviting assists to his teammates or to aim towards the goal, even finding the way to the goal thanks to a strong and precise shot.