There is currently no way to indicate task logic to players outside of having them [F3]+[H] or by spelling it out in the quest description that doesn't always get read (a frustration for another day).

A great fix would be to simply put the task logic inside of the quest pages, right next to the task type title. As an example, if there was a Retrieval Task, at the top right where it says "Retrieval Task" it would also say right next to it "(AND)" or "(OR)," with a mouse-over pop up describing what that means to the player ("You have to complete all tasks" or "You only have to complete one task").