If waterfall is plotted, how to read the value of a specific waterfall slice?

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

This is set from the waterfall plot type settings Plot->Plot Type Settings->Waterfall….

On the right part of the Active Plot Type toolbar (see figure above), the buttons  and  can be used to move upwards and downwards and select the time slice. The selected time slice from which the values are read from is plotted in green color.

Note: If you have turned on the cursor from Plot->Layout->Cursor… to read out the cursor values, you should also turn on Plot->Solo Curve. This will remove the slices in front of the active slice as shown in the figure below (the one with the green slice in front is there the Solo Curve feature is used).