ServerScriptService.Scripts.Testing:5: '=' expected near 'in'?

In your script you did

for_.n in pairs(workspace.Course.Paths:GetChildren()) do 
    source[n.Tag.Value] = n 
end

You did "for _.n" instead of "for _, n"

Example :

for _, n in pairs(workspace.Course.Paths:GetChildren()) do 
    source[n.Tag.Value] = n 
end

It's a syntax mistake. Putting a period instead of a comma tells Lua to check for an index in the given table, which requires an equal sign to be applied to a number before the index in the loop in a numeric for loop. For example, this is a generic for loop...

local numbers = {1, 2, 3}
for _, number in pairs(numbers) do
    print(number)
end

...but this is a numeric for loop:

local var = {number1 = 0, number2 = 0, number3 = 0}
for i = 1, var.number1 do
    print(i)
end

A comma is used in for loops to separate the two variables from each other. Using a period makes the compiler try to index the second variable.

As everyone else said:

It's a syntax mistake. Putting a period instead of a comma tells Lua to check for an index in the given table, which requires an equal sign to be applied to a number before the index in the loop in a numeric for loop. - BashCaster

And

You did "for _.n" instead of "for _, n" - voidstaronyt

But what your also forgetting is the "i" in "ipairs". The difference what it returns. "ipairs" returns index-value, while pairs returns key-value. You can read more about the difference between "ipairs" and "pairs" here which I found helpful in this explanation.

local enemyai = require(game.ServerScriptService.Modules.Classes.Enemy.EnemyAi)
local source = {}

for _, n in ipairs(workspace.Course.Paths:GetChildren()) do 
    source[n.Tag.Value] = n 
end

source["StartingPoint"] = workspace.Course.Other.StartPath

spawn(function() 
    while wait() do 
        enemyai.StartEnemy(source,"Regular") 
        wait(3) 
    end
end)

Also doing "while wait() do" before a spawn function is just bad practice (unless you have a really good reason for it) because its creating a new thread everytime it repeats its self, which eventually will cause performance issues.