The event on the first anniversary of his death will begin at 1:14 p.m. (1014 GMT), the exact time Khashoggi walked into his country's diplomatic mission to get documents to marry his Turkish fiancee Hatice Cengiz.
Cengiz, 37, will return to the building where she waited outside for him for several hours a year ago before raising the alarm of his disappearance.
Khashoggi, a Washington Post contributor hailing from a prominent Saudi family, entered the Saudi consulate on Oct. 2, 2018, to collect a document that he needed to marry his Turkish fiancee. Agents of the Saudi government killed Khashoggi inside the consulate and apparently dismembered his body, which has never been found.
The scheduled attendees at the service include U.N. special rapporteur on extrajudicial killings Agnes Callamard, who investigated the murder, and Yemeni Nobel peace laureate Tawakkol Karman.
No one has been held accountable for Khashoggi's death, although Turkish and Western intelligence agencies say the order to kill him could only have come "from the highest levels of the Saudi government."
Saudi Arabia has charged 11 people in the slaying and put them on trial, which has been held in secret. As of yet, no one has been convicted.
The kingdom's de facto ruler, Crown Prince Mohammed bin Salman, told U.S. broadcaster CBS Sunday that he did not order the murder, but took "full responsibility as a leader in Saudi Arabia."
Callamard responded on Twitter: "There is in this statement an implicit recognition that the killing of (Khashoggi) was a State killing. It happened under his watch as quasi head of state. The State is therefore implicated as he is."
Cengiz told dpa that although Khashoggi disagreed with the crown prince and the kingdom, by killing him "they are now faced with much greater problems. And they're going to pay the price for this."