Khashoggi, a Washington Post columnist, disappeared inside the Saudi consulate in Istanbul.
"Don't worry", Prince Mohammed is heard saying in English to the French leader, who responds, "I do worry".
Already the French Presidency has said that Emmanuel Macron spoke to the Crown Prince on the summit's sidelines about both the journalist's murder and Saudi's role in the war in Yemen, which the United Nations has called the world's worst humanitarian crisis.
Mr Trump later said there was "no discussion" but did not rule out holding longer talks with the crown prince during the two-day summit.
Russian President Vladimir Putin and bin Salman shared a chummy, enthusiastic greeting, beaming widely and clasping hands in something of a cross between a handshake and a high-five.
NEW DELHI/CAIRO -Crown Prince Muhammad Bin Salman met Indian Prime Minister Narendra Modi and told him about plans to scale up investments in India's tech, farm and energy sectors, an Indian official and the Saudi news agency (SPA) said on Friday.
Tunisia protests against Saudi crown prince's visit
TUNIS - Saudi Arabia's Crown Prince Mohammed bin Salman arrived in Tunisia on Tuesday, a Tunisian presidency source said. The protests were in sharp contrast with earlier parts of his tour of allied countries in the region.
Macron told Prince Mohammed that Europeans wanted global investigators to take part in the probe on Khashoggi's death and stressed "the necessity of a political solution in Yemen", the Elysee Palace said.
Last week the US President said "it could very well be that the Crown Prince had knowledge" of the planning and execution of Mr Khashoggi's murder, but that the US meant to "remain a steadfast partner of Saudi Arabia".
Trump, in an exclamation point-heavy statement before the summit, said it did not matter whether Prince Mohammed knew about Khashoggi's death and that Saudi Arabia was important for business and for its hostility to Iran.
Later Friday, a White House official said Trump and Prince Mohammed exchanged pleasantries at a leaders' session - as the president did with almost every leader in attendance.
The U.S. president also didn't pay much attention to Russian President Vladimir Putin, who found himself snubbed for the second time in a month after Trump used Twitter to torpedo their planned meeting in Argentina.
The two leaders also explored investing in solar energy through Softbank's Saudi-backed Vision Fund and opportunities to export Saudi non-oil products to India.
"We might [later], but we had none", President Trump told the press pool.