There are two types of collectibles that can be found within the Nightfall DLC.
Classified Intel: These are randomly picked up from searchable items, and their locations change during every playthrough. You will need to pick up a total of 6 of these intel types to unlock them. Only 1 player can pick it up, and it will automatically unlock the intels in order. Each area will contain between 1-2 intel items, and this can easily be boosted solo using the first area and then dying during the first drill section.
Encrypted: These are also permanent laptops that can be found on the map, and their locations are as follows:
Treason - Area 2: Once entering Area 2, use the stairs to the right hand side, and follow the balcony around to find the laptop on the ground.
Security Breach - Area 2: From the entrance, head to the left side to find a container with a fire trap next to it. Jump on the fire trap, then onto the container. Now, with your pistol, get a running start and run towards the nearest rooftop. Jump towards it and use the button to get up. Find the laptop on this roof near some fencing.
Exfil Denied- Area 3: Upon entering the Facility, there is a small booth on the left side, with some crates next to it. use the crates to get on top of the booth, and find the laptop here.
Sabotage - Area 3: Upon entering the Facility, use the large ladder to get to the 3rd story on the outside of the area. Follow the scaffolding around the perimeter and jump over the broken section to find the laptop on the ground.
The Ark - Final Area: During the final boss battle, if you run all the way across the area from where you enter, you will see a small toll booth. On the ground inside this toll booth, you will find this laptop.
Lastly, you must also complete Nightfall to unlock the Epilogue Intel. You can check your progress in the Extinction main menu, and there is a tracker available in the top right corner of the screen showing how many items you have collected. Collecting all the intel will unlock the following CUTSCENES.
i got all 15 as well plus watched all the vids and still didnt get it. anyone know why msg me online if you want. im curious cause it doesnt say in nightfall does it mean in all the dlc's to come then?
The achievement Undiscovered Truths is currently glitched and will not unlock upon completion. Mostly all players that collected all intel in Nightfall haven't unlocked the achievement. Hopefully, Infinity Ward will patch this.