How would I load a level/scene/mission by talking to an NPC?

What I want to do is this: NPC Bob has missions, the player talks to NPC Bob to select a mission, the player then goes to something like a sign or gate, the player then selects this sign or gate to finally load the mission which is on a different map.

How would I go about this? Also what would be the best way to go about loading the same map, but with different things in it? What I mean is, multiple missions use the “city” map, but each mission will load in different enemies and items. Do I use a scriptable object?

This is how to load/unload scenes and keeping certain game objects with the new scene manager functions … Unity - Moving Objects Between Scenes - YouTube

specifically to create a “city” map with different missions – create a scene that is the “city” map with all the models/buildings etc. Then create another scene (example “mission 1”) and make sure both are loaded at the same time in the editor by loading one and then right clicking on the other and selecting “load scene additive”. Then in the “mission 1” scene, add all your npc characters and items required for that mission. When playing the game, watch the video i made to learn how to load levels additively and load the “city” scene and then additively load the “mission 1” scene, or load “mission 2”, “mission 3” etc. the “city” scene contains all the building models and always remains the same while the mission scene changes depending on the quest. its like creating a base photoshop layer, and then overlapping another layer of whatever characters and items are required for the mission.