“je sais” is pronounced [ʒə sɛ]. The “je” is pronounced like “zhuh” with a soft “j” sound. “sais” is pronounced like “say” with a soft “s” sound and ending with a short “ee” sound. For example, you can think of it as similar to saying “I know” but with a French twist. Practice pronouncing it slowly at first, then gradually speed up as you get more comfortable. Listen to French speakers or language learning resources to get a better feel for the correct pronunciation.