Which double bond will react with m-CPBA to form an epoxide?
When two or more double bond are present then the more electron rich double bond will epoxidise. In above example the double bond containing the methyl group  has  electron donating  inductive  effect while the double bond containing the methoxy group  will have an electron donating resonance effect. The resonance effect is dominant over the inductive effect. Therefore the double bond containing the methoxy group is more electron rich. Therefore epoxidation occur on it.