To unlock the Everybody Benefits trophy in Assassin's Creed Odyssey, you must first complete episode one of the game when you leave Kephallonia and obtain your ship.
Once you complete episode one, travel to the island of Kos. You will find the first quest marker called A Business Opportunity for the Markos' questline in the Highlands of Asklepiades region at the Artemsia Fort (recommended level is 27).
Complete the following four quests and you will unlock the Everybody Benefits trophy:
A Business Opportunity
Old Friends, Old Problems
Farm In Flames