There are 13 challenges to choose from this year.
Unlocking a Skill Challenge requires you to complete Gold Level.
The easiest one I found was goalkeeping, which requires you to make a number of 1 v 1 saves.
Other notable straight forward challenges include dribbling and shooting. Everyone has different skills, and getting everything to gold level is a requirement for the Silver Lining achievement, so going for this should show you what Skill Game is most suitable for you.