"Well I just want them to be sure, because it's a pretty serious charge, and I want them to be sure," said Trump.
Trump added US intelligence was incorrect when it said Iraq possessed weapons of mass destruction, a part of what lead to a US invasion of Iraq in 2003. He called the invasion "a disaster, and they were wrong."
Trump said it was unfair to accuse Russia of hacking if there is doubt, saying he knows "a lot about hacking" and "it could be somebody else."
"I also know things that other people don't know, and so they cannot be sure of the situation," said Trump, telling reporters they would find out Tuesday or Wednesday what he knew about hacking.
Trump noted he was open to meeting with Taiwanese President Tsai Ing-wen. The two exchanged a controversial phone call after Trump's victory, breaking more than three decades of the "one-China" policy.
"I'm not meeting with anybody until after January 20th because it's a little bit inappropriate from a protocol standpoint. But we'll see," said Trump, who becomes president on January 20.
As for his New Year's resolution, he harped on his campaign slogan: Make America great again.
Before the New Year's celebration, Trump also took to Twitter to wish happy New Year "to all, including to my many enemies and those who have fought me and lost so badly they just don't know what to do."