Before Voldemort's death
Harry has a vision through Voldemort's eyes of Draco being forced to torture Rowle.
“More, Rowle, or shall we end it and feed you to Nagini? Lord Voldemort is not sure that he will forgive this time. . . . You called me back for this, to tell me that Harry Potter has escaped again? Draco, give Rowle another taste of our displeasure. . . . Do it, or feel my wrath yourself!”
A log fell in the fire: Flames reared, their light darting across a terrified, pointed white face — with a sense of emerging from deep water, Harry drew heaving breaths and opened his eyes.
He was spread-eagled on the cold black marble floor, his nose inches from one of the silver serpent tails that supported the large bathtub. He sat up. Malfoy’s gaunt, petrified face seemed branded on the inside of his eyes. Harry felt sickened by what he had seen, by the use to which Draco was now being put by Voldemort.
*Harry Potter and the Deathly Hallows, Chapter 9, A Place to Hide
Clearly, Harry is horrified by what Voldemort's doing to Draco. He feels sickened by the use to which Draco was being put by Voldemort. Why would he feel sick? He knew Draco wasn't happy becoming a Death Eater.
After Voldemort's death
The Death Eaters were rounded up and put into Azkaban. Seeing that Harry became an Auror and Draco didn't go to jail for being a temporary Death Eater, we can put two and two together and say that Harry knew Draco was redeemed.
[...] as the morning drew on, that the Imperiused up and down the country had come back to themselves, that Death Eaters were fleeing or else being captured, [...]
*Harry Potter and the Deathly Hallows, Chapter 36, The Flaw in the Plan
Draco also appears in the Epilogue at King's Cross to send off his son to Hogwarts. He acknowledges Harry, who in turn doesn't go and punch Draco in the face.