Jackie couldn't have forgotten everything.
In the movie, he gets a lot of flashbacks. For instance, when he was being interrogated by an agent of law enforcement, the agent started spinning around a key in his hands. When Jackie saw that rotating motion, he remembered that he was in a helicopter before, due to the rotating choppers being similar to the spinning motion of the key. So, it's possible that he remembered his father's saying through an unshown flashback.
Also, Jackie didn't forget everything. He was able to recognize a gun that was disguised as a camera by Christine(CIA agent who posed as a reporter). So, he remembered his training at the CIA. So, it's quite plausible for him to remember his father's saying, to whom he could have been emotionally attached to.
Always do these right thing. Stop the people who don't...Respect Nature-His father's anecdote