I Got Skills
Unlock all Skills.

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To access the skills screen, press options, "Character Customization", then "Skills". Skills are broken up into 4 categories; Melee, Ranged, Stealth and Health. To unlock skills, you need "Sync Points". You obtain sync points by:

Completing Main Missions
Completing Co-op Missions
Collecting the Sync Point Collectibles Found in Co-op Missions
In order to get this trophy, you need to purchase every skill in the game. In order to do that, you need to complete all of the aforementioned things as there won't be any spare sync points. So you want to complete all the main missions and co-op missions, then find all 40 of the Sync Point Collectibles hidden in the co-op missions. Once you have done that, you will have enough to upgrade all of your skills. Below is a list of all skills in the game that you need to buy. Also, if you are having trouble finding the sync points here is a video that shows the location of all 40: