Southampton Jankewitz signed his first professional contract in July 2019. On 19 January 2021, he made his first professional appearance for
Saints in a 2–0 home victory over
Shrewsbury Town in the
FA Cup. On 30 January 2021, Jankewitz made his Premier League debut as a substitute for
Oriol Romeu in a 1–0 home defeat by
Aston Villa. On 2 February 2021, he was sent off on his first Premier League start within the first two minutes of the away game against
Manchester United, for a dangerous tackle on
Scott McTominay. Southampton went on to lose the match by a record-equalling score of
9–0. After the defeat, Jankewitz was subjected to racist abuse on social media, which Southampton passed on to
Hampshire Police.
Young Boys On 12 July 2021, Jankewitz joined
BSC Young Boys for an undisclosed fee.
Loan to St. Gallen In January 2022, he joined
St. Gallen on loan until the end of the season.
Return to Young Boys and loan to Thun After returning to Young Boys, Jankewitz made several substitute league appearances and was a starter in three
Conference League qualifying games. After Young Boys failed to qualify for the group stage of the competition, on 30 August 2022 Jankewitz moved to
Thun on loan.
Loan to Winterthur On 8 June 2023, he joined
FC Winterthur for another loan spell. ==International career==