Prepare a shallow dish or glass container where the jelly can set. In a medium saucepan, combine the agar-agar powder, water, pandan extract, and sugar. Stir the mixture continuously over medium-high heat and bring it to a boil. Let it boil for 2-3 minutes, ensuring the sugar dissolves completely and the agar-agar is evenly distributed. Carefully pour the hot mixture into the prepared dish, spreading it evenly. Allow it to cool before transferring to the fridge to set for at least 2 hours or overnight. Once firm, cut the jelly into small cubes.