If I understood your requirements correctly, you want to get values from GridBoundColumn in GridTableView within DetailTables. If that is your requirement, please refer to the attached sample page and where you will find how to get values from nested table views.
Furthermore, you could have a look at our online documentation for accessing rows and cells in RadGrid and in particular for your scenario the "Accessing Table Views in a Hierarchical Grid":
Hope that helps.
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