I'm not sure what you intend with SUM, because Checkboxes are True o False.Did you mean Count, instead?
However you can discovery the value of each checkbox with this code:
Code:
Option Explicit
Sub Esamina()
Dim n As Long
Dim s As ContentControl
For Each s In ActiveDocument.ContentControls
n = n + 1
Debug.Print n, s.ID, s.Checked
Next
End Sub