Gumennik began learning to skate in 2006. In March 2014, he won gold at the Russian Youth Championships – Younger Age. The following season, he placed fifth at the Russian Junior Championships and repeated as the champion at the Russian Youth Championships – Younger Age.
Veronika Daineko became his coach in 2017. Gumennik won the silver and bronze at the Russian Cup 2017-2018 stages, won bronze at the Russian Cup Final, finished eighth at the 2018 Russian Junior Championships and won silver at the Russian Youth Championships – Elder Age.
2018–2019 season
Coached by Daineko and Vladislav Sesganov, Gumennik started his season with a gold medal at the 2018 JGP event in Vancouver, Canada. He ranked fourth in the short program but won the free skate and outscored the silver medalist, Tomoki Hiwatashi, by a margin of about seven points. At this event he scored his personal best score of 220.04 points and his free skating score of 150.35 points was the junior men's new record score. At his second JGP event of the season he won another gold medal, now in Ljubljana, Slovenia. He was ranked first in both the short program and the free skate, and again he beat the same silver medalist, Tomoki Hiwatashi, this time by about 4 points. With two JGP gold medals Gumennik qualified for the 2018–19 Junior Grand Prix Final, where he won the silver medal after placing third in the short program and second in the free skate. In January, he took gold at the 2019 Skate Helena. In February 2019, Gumennik won the silver medal at the 2019 Russian Junior Championships after placing first in the short program and fourth in the free skate. Assigned to the 2019 World Junior Championships, he was fourth in the short program with a new personal best, and eleventh in the free program, and tenth overall.
2019–2020 season
In the 2019-2020 season, Petr Gumennik remained on the Russian junior figure skating team, coached by Veronika Dainek, Alexander Ustinov and choreographer Nikolai Moroshkin. On August 5 and 6, at the open skates of the Russian junior team in Novogorsk, Gumennik showed new short and free programs. Both programs were choreographed by Nikita Mikhailov. Gumennik said his goals for the season were to qualify for the JGP Final and win a medal at the Junior World Championship. He also said he planned to move to the senior level the following season, and would attempt three quads in the free program, two Salchows and one Lutz. Beginning the season on the 2019–20 Junior Grand Prix, Gumennik won the gold medal at the event in Chelyabinsk, Russia. At this event he scored his personal best score of 222.14 points and made his first attempt at the quad Lutz, which ended in a step out. At his second event in Egna, Italy, Gumennik placed second behind Daniel Grassl. He then competed at the senior level at the 2019 CS Warsaw Cup, winning the silver medal. Qualifying for the Junior Grand Prix Final, he placed fourth in the short program after falling on his opening triple Axel. He was fifth in the free skate after falling on his quad Lutz attempt and underrotating three other jumps, and placed fifth overall. Speaking afterward, Gumennik noted "I’ve had a difficult season because I grew a lot and I’ve had a lot of pains in my legs and back. This made it hard to skate my program well." He nevertheless said he felt "very positive being here at the Final with the best athletes, they really inspire me." At the 2020 Russian Championships, Gumennik ranked third in the short program, with only a mirror spin error. Gumennik overslept and missed the morning practice session for the free skate, where he came tenth with errors on his quad Salchow attempts and dropped to seventh overall. After winning a silver medal at the Russian Junior Championships, Gumennik earned one of Russia's three berths at the 2020 World Junior Championships in Tallinn, Estonia. He placed ninth in the short program after putting a hand down on his triple Axel attempt, which he attributed to nerves. He placed second in the free skate, rising to the bronze medal position overall, only 0.63 points behind silver medalist Yuma Kagiyama. He called it "one of my best performances in international competitions." Since 2019, the consultant of Gumennik is Tamara Moskvina.
Programs
Records and achievements
Set the junior-level men's record of the new +5 / -5 GOE system for the free program at the 2018 JGP Canada. This record was subsequently broken by Stephen Gogolev.
