Khashoggi, a columnist for the Post, was strangled and dismembered at Saudi Arabia's consulate on October 2, 2018 when he went to obtain documents required for his marriage to Turkish citizen Hatice Cengiz.
She unveiled a memorial to Khashoggi directly in front of the consulate.
"After the worst year of my life I stand here broken but proud," she said in a speech.
"I still seek justice. I want to know what happened to his body. I want his friends to be released from jail. I want those in power to be held accountable for their actions."
The case has sorely strained the ultra-conservative kingdom's ties with the West and tarnished the image of Crown Prince Mohammed bin Salman. The de facto ruler, who is widely known as MBS, had tried to project an image as a reformer.
"A year ago he had the great and good eating out of his hand," said David Hearst, chief editor of Middle East Eye, opening the memorial service.
"(But) Jamal's murder became a nightmare for his killer. In sealing Jamal's fate, Mohammad bin Salman, the Crown Prince of Saudi Arabia, sealed his own."
Amnesty International's Andrew Gardner called for a UN-led investigation into the murder, denouncing the "sham" trial in Riyadh as "a mockery of justice".
Eleven suspects have been put on trial in Riyadh, five of whom face the death penalty, but hearings are held behind closed doors and the names of the defendants have not been released.
A June report by United Nations Special Rapporteur Agnes Callamard said there was "credible evidence" linking MBS to the murder and an attempted cover up.
So far however, no UN nation has heeded her call to initiate a full investigation.
"We will not stop until justice is served," Callamard said at the ceremony.
The crown prince has denied any involvement but tells PBS in a forthcoming documentary that he accepts responsibility for the killing, because it happened "under my watch".
Bezos gave a short speech directed at Cengiz, saying: "You need to know that you are in our hearts. We are here and you are not alone."