✓ Accepted answer
You'll want to use magnitude to determine the closest part. Magnitude, in this sense, is essentially the length of a vector, and we want to find the shortest length. We'll arrive at this conclusion by subtracting the node's vector from the original position.
local OriginalPart = workspace.OriginalPart
local NodesFolder = workspace.Nodes
local Nodes = NodesFolder:GetChildren()
local Closest = nil
for i,v in pairs(Nodes) do
local magnitude = (OriginalPart.Position - v.Position).Magnitude
if Closest then
if magnitude < Closest then
Closest = magnitude
end
else
Closest = magnitude
end
end