Knies enjoyed a breakthrough season in the NHL for the Maple Leafs in 2024-25. He had 58 points (29 goals, 29 assists), which included his first NHL hat trick (with two assists) in a 6-4 win against the Boston Bruins at Scotiabank Arena on Jan. 4, and seven points (five goals, two assists) in 13 Stanley Cup Playoff games to help Toronto reach the Eastern Conference Second Round.

One day after Knies and the University of Minnesota lost 3-2 in overtime to Quinnipiac University in the NCAA Frozen Four championship game on April 8, 2023, the forward signed a three-year, entry-level contract with the Maple Leafs. He made his NHL debut the next day and had one assist in three regular-season games.

Knies had an assist and was plus-2 in his second NHL postseason game, a 4-3 overtime win against the Tampa Bay Lightning in Game 3 of the 2023 first round. He then scored his first NHL playoff goal in a 4-2 loss to the Florida Panthers in Game 1 of the second round.

Knies signed a six-year, $46.5 million contract to remain with the Maple Leafs on July 1, 2025, in lieu of becoming a restricted free agent, coming off a season when he set NHL career highs in goals (29), assists (29), points (58), power-play points (15), game-winning goals (six) and time on ice per game (18:31)

Toronto's second-round pick (No. 57) in the 2021 NHL Draft, Knies was a finalist for the 2023 Hobey Baker Award, given annually to the best men's player in NCAA hockey, after he had 42 points (21 goals, 21 assists) in 40 games. He was a unanimous pick for the Big Ten All-Freshman Team and a finalist for Big Ten Freshman of the Year after getting 33 points (15 goals, 18 assists) in 33 games.

Knies played two seasons for the Tri-City Storm of the United States Hockey League, where he had 31 goals and 56 assists in 90 games.