There are a total of 57 skills to unlock in Aiden’s Skill Tree (Online Skills don’t count). To purchase a Skill you'll need Skill Points which can be obtained by levelling up Aiden, which is done by completing story missions and Acts, taking part in the multiple activities Chicago has to offer, or simply finding collectables.For two Skills you need to complete City Games (NVZN to Level 5 and any Chess Puzzle to Level 10)
here is the Solution for the End Game Puzzle in Brewed (The Loop)
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Posted by PSYCHO POOCH: do not need to play chess till level 10...you only need to play 10 chess puzzles. Which could be 5 different ones to level 2. I played 3 types of chess puzzle and every one i did added to the counter
Posted by elKamikazeSqui: ... Should also mention that Gang Hideouts reward you with Skill Points for finishing them too.
Posted by Famous Yeti : For anyone that is short on Skill points: Go to Options > Gameplay > Reset Side Mission Content. You keep all your progress but you can redo the side missions (like Gang hideouts) to get more Skill points.