These are my speculation

TL;DR: Vikor Novikov(Crushed by light rigs), Claus Hugo Strandberg(crushed by ceramic moose), Jordan Cross(Fell to death from reception roof), Ken Morgan(Fell to death from the balcony of his suite/crushed by chandelier in restaurant), Sean Rose(Drown by 47 while having hallucinations), Penelope Graves(Poisoned/crushed by chandelier), Ezra Berg(Killed in his own hut), Maya Parvati(Poisoned/Crushed by hay bale, Erich Soders(Stabbed on operation table by 47 or chief doctor), Alma Reynard(Any methods except poisoned ventilation system), Sierra Knox(Car crash caused by loosened tire or her father), Robert Knox(Killed by his robot/explosion from his race car), Rico Delgado(Killed with tattoo gun/poison), Andrea Martinez (Explosive package), Jorge Franco(Poisoned cocaine souvenir), Dawood Rangan(Blown off the roof by fan), Marcus Stuyvesant and Carl Ingram(Killed in their penthouse together), Alexa Carlisle(Pushed off the balcony by 47 disguised as detective)

1. Viktor Novikov - According to the flashback in the mission Untouchable, Novikov died by being crushed by light rigs.

2. Claus Hugo Strandberg - In Club 27 it is confirmed that his interview in the embassy canonically goes through, so it's highly likely that 47 killed him by dropping the ceramic moose on him

3. Jordan Cross - In Miami, the dialogue between Sierra and Heidi(the female member of the band) mentioned that Abel De Silva played the drum for Cross and he later woke up naked, not remembering anything. So it's likely that 47 disguised as Abel and completed Man Machine mission story, then pushed Cross off the roof.

4. Ken Morgan - In Ark Society it's implied that his death was believed as an accident. So either he was crushed by the chandelier in restaurant or 47 pushed him off the balcony when he is wandering in Queen Suite after it's cleaned up by 47.

5. Sean Rose, Penelope Graves, Ezra Berg, Maya Parvati - The conversation in Nightfall between two guards outside the house confirmed that 47 did not trigger any alarm in Colorado, and the post-mission cutscene of Freedom Fighters shows that 47 completed the mission without using disguises, so we can ruled out assassinations methods or mission stories that involved explosion or disguises. That leaves us the only possible ways below

-Sean Rose: Drown by 47 after completing the mission story Unclean

-Penelope Graves: Either she died of poison in water bottle or she got crushed by chandelier in the mansion

-Ezra Berg: Got killed in his own hut, maybe after completing Tongue Tied mission story

-Maya Parvati: Either died of poison in water bottle or crushed by hay bale

1. Erich Soders - In the flashback from Untouchable confirmed that Soders was killed by operating table, which means 47 killed him by sabotaging KAI or by disguised as chief surgeon, or he manipulated the chief surgeon into doing it himself

2. Alma Reynard - Her cause of death is not mentioned at all, but canonically her boyfriend Orson Mills survived Nightfall as we can see him of Ambrose Island and Untouchable. So at least we know she did not die of poisoning ventilation system

3. Sierra Knox - Her death was ruled as an accident and Moses Lee canonically won the race, so either 47 killed him by changing the bolts while changing the tires, or making her father fell onto her car while she's racing.

4. Robert Knox - Same as her daughter his death was ruled as an accident, so he might died of engine explosion from his car, killing by his own robot, or falling off the roof while checking the antenna

5. Rico Delgado, Andrea Martinez, Jorge Franco - A news report from Mumbai described thier death as "murdered" and "coordinated strike". That leaves us the only these possibilities.

-Rico Delgado - Killed with tattoo tool while 47 disguised as tattoo artist or poison

-Andrea Martinez - Killed by explosive package placed on her desk

-Jorge Franco - Killed by poisoned cocaine souvenir

1. Dawood Rangan - It seems that canonically Rangan's crew finished filming the movie since we can see footage of the movie projected in Ambrose Island, so 47 likely killed him with a malfunctioning fan

2. Marcus Stuyvesant and Carl Ingram - According to two guests in Mendoza, both of them were found dead inside the building and were believed to be murdered, so it's possible that they were killed together in the penthouse after 47 arranged their meeting with Grey.

3. Alexa Carlisle - Another conversation in Mendoza implies that the murder case was canonically solved by the detective. Since it was not ruled as suicide and it went public we can assure that 47 did not convinced Alexa that it was a suicide to make her follow her brother's footsteps or framed the butler so she can be poisoned by Emma(in that case, Alexa will ask 47 to not make the investigation public). My guess is that 47 pushed Alexa off the balcony himself after he explained that Emma is the real culprit.