You can use player:DistanceFromCharacter() which returns how many studs away is the vector3 from the player.
put the parts in a folder and try something like this:
local NearestPart = nil
local Lenght = nil
local Folder = workspace.Folder
local Player = game.Players.LocalPlayer
wait(10)
for i,v in pairs(Folder:GetChildren()) do
local LenghtX = Player:DistanceFromCharacter(v.Position)
if Lenght == nil or LenghtX < Lenght then
Lenght = LenghtX
NearestPart = v
end
end
print(NearestPart.name)
This script prints the name of the closest part after 10 seconds.
The NearestPart will be the nearest part to the player inside of the folder.