Ther are two things that define wheter a molecule is polar or not polar. First we have to decide if the bonds are simetrical or asimetrical. Simetrical bonds only occur when they are inbetwen two equal atoms. This is not the case since we have two bonds: K-S-K. The next step is to identify the structure of the molecule, because asimetrical bonds in oposite directions will calcel each other out. So lets see the structure of this molecule:
Sulfur atom needs 8 electrons to be stable. Sulfur has 2 electrons for each K-S bond. So we have 4 there. we need 4 more. They are in 2 unbonded orbitals. 2 electrons in each orbital. The repulsion forces between unbonded orbitals are grater than bonded orbitals. This causes the molecule to form and angle and therefore the polarity of the asimetric bonds do not cancel each other which means we have a polar molecule. This is the very same process that hapens to the water molecule