Wis. Stat. § 889.242: How, when witnesses dead.

If any grantor residing in this state refuses to acknowledge the grantor’s conveyance and all the subscribing witnesses thereto are dead or out of the state, it may be proved before any court of record by proving the handwriting of the grantor or of any subscribing witness, upon the court first summoning the grantor to hear the testimony as provided in s. 889.241.