Code Book Location: The Codebook for the last Vox Code Puzzle is located in the Financial District (just next to the bank), inside a burning Hudson's Clothing Shop:
Enter the ruined store and jump down to the cellar, to find the Code Book near a sink in the corner:
You will find the Vox Code in the Bank of the Prophet. Go through the door with the green light on it that is to the LEFT of the vault. NOT the one on the right.
Pass through this corridor:
and turn LEFT and then right
(basically you will navigate through the leftward hall in the bank's main hall )
Arrive in a small room in the read which has a corpse and the red writing that spells "Hoarder" on the wall:
Elizabeth decrypts the vox cipher to read: "type...three...letters...to...spell...the...voice"
Enter the code "VOX" on the typewriter to reveal a secret vault with goodies