Could a bronchoscopy tell what caused wegener's granulomatosis?

No it cannot: A bronchoscopy is useful for identifying that wegener's is affecting the lungs but it will not tell you the cause. Wegener's is in a class of conditions known as autoimmune. This is where the body does not recognize its own cells as being "self". In turn an immune response causes inflammation in the lungs, eyes and sinuses (the classic locatioins in the body to be affected by wegeners).

No: Bronchoscopy and biopsy gets tissue for examination. The look around can identify narrowing or surface lesions of the tracheobronchial mucosa=surface. Small biting biopsy of surface or lesions are diagnostic tools.

Nothing can: It's a mistake to try to figure out what "caused" Wegener's. It simply happens. Once uniformly fatal, thanks to Dr. Wegener's work and what came after, we can now manage the disease so most people survive and eventually recover. He was in the wrong place at the wrong time, but was one of the great physicians of the 20th century. Wishing you a speedy recovery.