Objects positions in an Array

Hey there, im pretty new into Unity and specially into coding. im good with basics of C (from my study).

As i cant find any good tutorials on this matter and cant find my answers from google i wanted to ask here.

so im building a RTS like Game, i want to pseudo randomize the levels later on. (Like Forest can be on X Positions with X diffrent Shapes and X Different Trees, so predefined Positions) But there hasnt to be a Forest after all (At this positon)

The gatherer wont be player controlled so i want the AI to find the nearest position of tree from his own position. Thats why i need (as far as i understand coding) all the positions of every tree.

So i wonder how to save different positions/transforms of an prefab into an array. So i can sort these transforms for the nearest.

What would i need to do, do a small script on every prefab which calls out its own position for an empty gameobject script?

Any ideas how to approach this and what to read about it?