Chapell registered a double in the space of six second-half minutes at Northampton, to wipe out Jacob Blyth's first-half goal and inflict a 2-1 loss on the Cobblers.
Blyth had put the hosts in front at Sixfields when he headed home one of several fine Danny Emerton crosses.
But Torquay improved markedly after the break and carved out a number of chances, two of which were taken with great aplomb by former Sheffield United wide man Chapell.
"We're obviously delighted," said Knill. "It was a game of two halves and it felt like we were totally dominated in the first half but I think when we look at it again we'll see that we weren't.
"That's three times we've come back from a goal down this season and that shows real character.
"Jordan (Chapell) has got three for the season now; we've set him targets and he's right on track with all of them.
"As with all wide players, the thing that makes them different is their ability to put the ball in the back of the net. Both of his goals were great finishes.
"I'm really pleased for him. He's one of those players you don't notice is around sometimes. He's so low maintenance, he just comes in, does his work and then comes in the next day.
"I'm pleased he's getting his rewards and those rewards come from hard work on the training ground."