In Chapter 37, DeWitt and Elizabeth reach the top deck, where Comstock is located because they are looking for some answers.
Engineering Deck is the last chapter of the videogame where players can find the remaining BioShock Infinite collectibles, and the following collectibles guide reveals their exact locations in the interior of the flasghsip.
Go across the ships interior after the big battle to find the second sky-line available in the area. Use it to reach a higher platform and head back inside the ship.
Find Comstock, and after you deal with the situation use the stairs to reach the lower catwalk.
Before heading on the higher catwalk that leads behind the mural/painted glass (where theres no turning back if you reach the control room and use the ships controls), check Comstocks office (the office is right above the statue representing the siphon).
On the desk is the first BioShock Infinite Engineering Deck Voxophone.
THE MIRROR OF SIN; Zachary Hale Comstock; June the 21st, 1893
From the catwalk mentioned above you can also gain access to Comstocks bedroom (the catwalks in this area are symmetrical and so are the entrances to the office and the bedroom).
From the bed inside you can pick up the second BioShock Infinite Engineering Deck Voxophone.
This Voxophone is also the last one in the game, so if you followed our complete guide you should be rewarded with the Eavesdropper achievement/trophy.
THE PROPHET IS DYING; Rosalind Lutece; December the 4th, 1907
Now, you can follow the higher catwalk inside the control room.
From now on you just have to follow your objectives to complete the game, because the next two chapters, Command Deck and The Sea of Doors, don’t feature any BioShock Infinite collectibles.