How to write command in debug mode?

I need to debug a function, and to do it I would like to display variables, do few computations etc while I am at a breakpoint.

But I don't see where I could do that ? I have the stack window opened but I can't write anything in this.

To give you an idea, I have a complex number and I want to understand why it is complex so I would like to check many variables while in debug but I don't want to write things in the function before the debug and then show them.

I want to directly write what I need to display while I am in debug mode without having predicted what I needed to display before launching it.

In particular, I suggest you look at Dialog. It allows the kind of interaction you describe.