If waterfall is plotted, how to read the waterfall slice values using the cursor?

This is only supported if the waterfall layout mode is Separate lines waterfall as shown below.

This is set from the waterfall plot type settings by typing F5, or Plot->Plot Type Settings->Waterfall…).

On the right part of the Frequency Plots Toolbar, the buttons and can be used to mover upwards and downwards and select the slice. The selected slice from which the values are read from is plotted in green.