Is emphysema common for nonsmokers?

No. However, if some one has a genetic predisposition to emphysema, such as alpha-1-antitrypsin disease, then they can develop emphysema. Also, people who are exposed to second hand smoke on a chronic basis can develop emphysema.
No... COPD is not common in non-smokers but it can occur. The diagnosis includes alpha-1-antitrypsin deficiency, which is caused by an enzyme deficiency. Treatment includes replacement of the enzyme to avoid lung as well as liver disease or to slow progression of disease, if present as well as treatment of any lung or liver disease that is present at time of diagnosis. Diagnosis is made via a blood test.
No. There are genetic predispositions for emphysema but even in those cases the patient is chronically exposed to smoke. Recent data has demonstrated that anorexia nervosa can predispose to emphysema and premature birth.
No. It is rare for non smokers to develop emphysema (usually it is caused by occupational exposures in non smokers or genetic deficiecy such as Alpha one antitrypsin).