Jonck attended Hoërskool Roodepoort, where he not only played rugby for the first team, but also took part in Greco-Roman wrestling. However, he then moved to Wellington, New Zealand, where he joined Swindale Shield side Poneke. He represented the Poneke Colts team in 2011 and appeared for their first team in 2012. He was also a member of the ITM Cup side 's Under-20 and Under-21s teams.
Wits / Falcons
He returned to South Africa in 2013 to play rugby for the University of the Witwatersrand. He made one appearance for team newly promoted from the Varsity Shield into the 2013 Varsity Cup competition, starting in their 0–52 loss to. He started six of their seven matches in the 2014 Varsity Cup – scoring a try in their 15–32 defeat to Johannesburg rivals – but his side lost all their matches in the competition for the season year in a row to be relegated back to the Varsity Shield for the 2015 season. However, Jonck joined Kempton Park-based side for their 2014 Currie Cup qualification campaign. He made his first class debut by starting in a 54–40 victory over the in Round Four of the competition and also started their 25–40 defeat to and came on as a replacement in their defeat to the in their final match. The Falcons finished in sixth position on the log, resulting in them playing in the 2014 Currie Cup First Division. Jonck started their matches against the, and the, helping them to finish in fourth position on the log and clinching the last semi-final berth. He started their semi-final as the Falcons caused an upset by beating a Leopards side that finished top of the log 31–24 in a match in Potchefstroom. He also started the final, but ended on the losing side, as a 23–21 victory by the saw them win the titlefor the first time in six years.
College Rovers / NMMU / Kings
In 2015, Jonck was named in the College Rovers squad that participated at the 2015 SARU Community Cup. However, he failed to make any appearances for the KwaZulu-Natal club side in this nationwide competition. He was then named in the squad for the 2016 Varsity Cup and was earned inclusion in the training squad for Super Rugby side the, being named on the bench for a pre-season friendly match for the.
