If he discovers the truth, there's no knowing what ______ happen.

Let us explore the given options: The modal 'might' is used to express possibility.The modal 'would' is used to talk about hypotheses (when we imagine something). The modal 'should' is used to express mild obligation or advice. The modal 'shall' is used for expressing a strong assertion or intention. Complete Sentence: If he discovers the truth, there's no knowing what might happen.