Jankto signed for
Udinese from
Slavia Prague in 2014 for a reported fee of €700,000. Without making his league debut for the team, he went on loan to
Serie B side
Ascoli in 2015, debuting on 15 September in a Serie B 1–0 home win against
Virtus Entella. On 6 July 2018,
Sampdoria announced that Jankto had joined the club on an initial loan deal with an obligation to make the transfer permanent for €15 million. On 12 August 2018, Jankto scored on his debut for Sampdoria in a 1–0
Coppa Italia win against
Viterbese. Sampdoria later made the transfer permanent. The following year on 10 August, he returned to his homeland after joining
Sparta Prague on a one-year loan deal. On 15 July 2023, Jankto signed a two-year contract with option with
Serie A club
Cagliari. He made his debut with Cagliari on 21 August 2023 in a goalless draw against
Torino FC. On 3 March 2024, he scored his first goal for Cagliari in a 1–0 victory against
Empoli. On 21 August 2025, Jankto announced on his Instagram that he had retired due to persistent health problems. He also referred to “wanting to spend more time with his son” as one of the reasons for his retirement. ==International career==