@alvita. The current version doesn't wire up component queries to the column's children. There's a post discussing how to do that here:
However, my first thought is that this isn't the right way to achieve cascading comboboxes. Rather than having the two comboboxes talk to each other directly just have the first combobox update the row's record when a value is selected. That'll cause a refresh of the row and you can render the second combobox based on the value in the record.