There are a total of 15 Agent DNA Orbs in the city to collect, each one unlocking a new character. A counter per zone is available on the map screen in the top right, and the orbs will stay on your screen even after you've collected them. You can find all 15 in the video below, with timelinks available as well.
[1:09] - 1 - Marshall - The Exchange
[1:50] - 2 - Anderson - Founder's Footsteps
[2:33] - 3 - Nikias - Khan's Scar
[3:08] - 4 - Varma - Dumping Grounds
[3:39] - 5 - Hicks - Picker's Pen
[4:16] - 6 - Lazar - Sulphur Spits
[4:46] - 7 - Petrov - The Refinery
[5:39] - 8 - Schmidt - Ashwood Marina
[6:40] - 9 - Baresi - Ashwood Marina
[7:32] - 10 - Cuan - Ashwood Marina
[8:10] - 11 - Mensah - The Vision
[9:34] - 12 - Walker - Southern Heights
[10:52] - 13 - Gadise - Southern Heights
[11:22] - 14 - Ramos - The Pantheon
[12:03] - 15 - Bartrom - The Pantheon