If you set a breakpoint and an application stops on it, you can move mouse over some variable and see the contained value.
You can evaluate any expression when application is stopped on breakpoint, simply select it, right click on selection, and in context menu click Evaluate expression.
You can also use Designer -> Main menu -> Debug -> Immediate window in debug mode. To run in debug mode click Main menu -> Debug -> Start debugging -> and select which mode to debug (in general Thin client: start debugging) when your configuration is opened in Designer mode.