He will need to file a tax return in both states, but will be able to request a refund for the taxes withheld in Wisconsin. These two states have a reciprocal agreement. Therefore, he can file an exemption form so that next year he can request to have taxes withheld by his resident state only. Please view the Turbo Tax FAQs below for more information.
https://ttlc.intuit.com/replies/4776822
https://ttlc.intuit.com/replies/3299954
