With the Delphi grids I mentioned, you have to query the underlying DataSet object (which is a property of the DBGrid) to get certain pieces of information. And in some cases, query the DataSet for an Index then use the Index to look up a separate set of records.
But these are specific to the control types and I had the Delphi developers on hand to explain how the control behaves.
You probably want to speak to a developer who has used the control.
There is no single answer for questions like this.
(I'm not sure about it being "just" a GUI as well. Surely you view and enter information via the GUI so it must be stored somewhere? It must have some sort of datastore ...)
For DB's, I usually just create a connection string and query it directly via my code. But again, you need to know the database in order to this. It's not something you can guess your way through really.