I'm not sure what you mean by arc fault rating. If you mean amps interupting capacity, you would find that information molded into the case of the breaker or printed on a small sticker attached to the breaker. If there are no markings, the AIC is 5000 amps. If you don't have the breaker in question on hand, the information is usually available in the manufacturers catalog.

Few things are harder to put up with than the annoyance of a good example.