Problem:

Your syntax for the pairs method is all messed up and also, if you want to just print what each of the values are when you call the function you would do the following. However, if you want to do something additional just comment below and tell me what else you want it to do and I will try my best to help you. I am going to comment through my script and will explain it the best I can...

Here is my script:

stocks = {KNG = 250, OCT = 1500, SHL = 2000, SNY = 4350, DEL = 8750, MCR = 25000} -- Your table which you set up. (Hopefully no explaination needed seeing as you set it up)

function newValue(stock) -- Your function with the parameter of 'stock'
        stock = stock + math.random(-(2*stock), (2*stock)) -- Your mathematical equation/solution
        return stock -- This returns whatever stock equals after the calculations.
end -- End for function above.

for _, each in pairs(stocks) do  -- This is where you might not know what to do. There are several ways to do the pairs method however, the easiest way to remember them is as two values which pretain to the table which is in the parenthesis.
    print(newValue(each)) -- This prints whatever the function up there returns. 'each' being the value. It gets the value from the table and then does the equation with that number and then returns it and prints it here.
end -- This end is for the pairs above. 

-- I saw that you printed the table out here. Which I have no idea what you were trying to accomplish there, however, if you wanted to print all the values inside of that table at the top you had to use the pairs method.... Just like the above one... 

Here is a website where you can learn more about the pairs method.

I hope I helped in one way or another and thank you for reading this answer. If you have any questions feel free to post a comment below.

~~ KingLoneCat