In hacked emails, Powell wrote: "Everything (Hillary Clinton) touches she kind of screws up with hubris," blunt comments that the the Bush administration secretary of state did not intend to go public.
"I have a great deal of respect for Colin Powell, and I have a lot of sympathy for anyone whose emails become public," Clinton said in response to a question from CNN's Don Lemon on the Tom Joyner radio show. "I'm not going to start discussing someone else's private emails. I've already spent a lot of time talking about my own, as you know."
Asked again, Clinton said: "I'm not going to comment on anything that is said in a private email."
Trump, meanwhile, took to Twitter Wednesday night to disparage Powell, seemingly in response to harsh words from the former Bush administration official.
"I was never a fan of Colin Powell after his weak understanding of weapons of mass destruction in Iraq = disaster. We can do much better!," Trump said.
Powell had written in June: "Trump is a national disgrace and an international pariah."
Clinton has had to repeatedly answer questions about her exclusive use of a private email server as secretary of state. At times, Clinton has indicated that Powell advised her to use private email instead of the State Department system.
"I have told Hilleary's [sic] minions repeatedly that they are making a mistake trying to drag me in, yet they still try," Powell wrote in another email.
Powell's emails were posted to DCleaks, a website known to share hacked documents associated with high-profile figures, and first reported by BuzzFeed and The Intercept.
An aide to Powell confirmed the accuracy of the emails to CNN but offered no further comment.
Powell's emails offer an unvarnished look at how the former secretary of state views one of his successors.
"For good reason she comes across as sleazy," Powell writes after being asked when he plans to endorse Clinton in the 2016 presidential race.
In other emails, Powell writes that the investigations into the 2012 Benghazi terrorist attack "is a stupid witch hunt" but that some blame rests on Clinton.
Clinton returns to the campaign trail on Thursday in North Carolina after spending three days at home after being diagnosed with pneumonia.
In the interview -- which was taped on Wednesday -- Clinton said she was "well aware that I still have work to do" to attract young black voters.
"I'm very committed to continuing to travel across the country, to talk about and hear from young African Americans about the struggles they face daily," she added.
Clinton also declined to answer whether she would ask for President Barack Obama to take back Merrick Garland's nomination to the Supreme Court should she win in November.
"I think we should stick with one President at a time," Clinton said. "I'm going to let this President serve out his term with distinction and make the decisions that he thinks are right for the country. I think he's got a pretty good track record, and he's earned that right."