sksks is a phrase that vsco girls use. A vsco girl is a girl who has a app called vsco and they act a certain way. They wills normally go Sksksksksk. Some people belive that sksksk actually stand for scaring kids but many people have different ideas. If I was you I would say don't worry about knowing what it stands for, you can just say it whenever you want, but the right moment would be when someone had either done something funny or stupid.
Look at her shirt it's so ugly sksksk