(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.
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.