Attack on Titan 2

About half way through chapter 1, after the events of Trost district, you will gain access to training. This is located in the Training Field area.
Talk to the soldier in the centre of the map to bring up a menu of the available options. Each of the three types of training upgrades two of your stats. You will need to use Wings of Freedom to train, but these are easily picked up, so this shouldn’t hinder you too much.
Performing training solo has a higher chance of success, but it takes longer to level up, whereas joint training has a higher chance of failing, but with greater gains.
You can increase the chances of success in joint training by improving your relationships with other characters.
I found joint training to be the quickest method for this. Just go through each of the categories and pick the highest success rated ally each time. Do this until all three bars are completely full and the achievement will unlock.

You will use wings of freedom to max out your training. You can either do solo or joint training, i found joint training to be the fastest and most successful. Everytime you do joint, the characters will change and their percentage as well. Just go through the list and see who has the most higher percentage to not fail.
PS: YOU CAN MAKE IT PAST 161 SKILL POINTS! THE MAX IS 200! See guide below