(there's) no knowing

There is no way one can be sure; no one knows or can tell. He's already very volatile at the moment—no knowing how he'll react to bad news like this. Unfortunately, there's no knowing if such an effort will actually translate to a meaningful, long-lasting improvement in the economy. The CEO acts so erratically that there's no knowing what she will do next.

(there's) no saying

There is no way one can be sure; no one knows or can tell. He's already very volatile at the moment—no saying how he'll react to bad news like this. Unfortunately, there's no saying if such an effort will actually translate to a meaningful, long-lasting improvement in the economy. The CEO acts so erratically that there's no saying what she will do next.

(there's) no telling

There is no way one can be sure; no one knows or can tell. He's already very volatile at the moment—no telling how he'll react to bad news like this. Unfortunately, there's no telling if such an effort will actually translate to a meaningful, long-lasting improvement in the economy. The CEO acts so erratically that there's no telling what she will do next.

there’s no ˈknowing/ˈsaying/ˈtelling...

it is impossible to know/say/tell: There is no telling what he may do when he gets angry. ♢ There’s no saying what will happen.

there's no knowing/saying/telling...