知れない

しれない【知れない】

〔わからない〕 there is no saying [knowing]; I don't know; I can't say [tell]; it is impossible to tell.

●いつどんなことが起こるやも知れない. There is no knowing [Nobody knows] what may happen at any time.

・君のことをどんなに心配したか知れない. You can't imagine how anxious I was about you.

・そんなことをするやつの気が知れない. I can't imagine what would make someone do such a thing.