A number of NPCs in Pokemon Sun & Moon ask me to do an errand then return. For example, I have met a scientist who wanted to me to return to him when I'd attained ten Pokemon 'caught' Pokedex entries.
The game doesn't seem to list these quests anywhere, so it's hard to remember what I've been asked to do (and where to go back to turn it in when I have done so).
How many of these people are there, where are they, and what are they after?