As Fabian said, Create Survey and Building objects in the nanoflow Create_NewSurveyObject and associate both of them in the same nanoflow. Then update your page like below. Then you can edit Number of building field.
First thing that I see here, is that your text box is still using the attribute from the outer `Building` data view.
Since the `Create_NewSurveyObject` nanoflow doesn’t seem to also create the associated `Building`, this data view therefor has no object, so the text box will be read-only.
The inner data view with the nanoflow will most likely allow you to get an editable text box, but if that created object is not associated to the outer `Survey` object, the changes will also get lost when saving.
I think the best option, given that this seems to be a page for a new entry, is to create the `Building` object in the `Create_NewSurveyObject` nanoflow as well, so that the association can already be set and both objects exist. However, this also assumes that both the `Survey` _and_ `Building` object are supposed to be new objects.
If you just want to be able to select existing objects, using a reference selector is probably the easiest, you could use a page to select the object, on which you can have a list view/grid with a new button should a new `Building` be desired.