Wis. Admin. Code Elections Commission EL 9.04
The vote of any absent elector may be challenged for cause by an inspector or by an elector and the inspectors shall have all the power and authority given them under ss. EL 9.01 and 9.02 to hear and determine the legality of the ballot the same as if the ballot had been voted in person. One of the inspectors shall administer the following oath or affirmation of veracity to the elector challenging the absentee elector's ballot: "You do solemnly swear (or affirm) that you will fully and truly answer all questions put to you regarding the challenged person's place of residence and qualifications as an elector of this election"; and shall ask the challenger if he or she is an elector and then shall ask only those questions provided in s. EL 9.01(2) which are appropriate to test the qualifications of the challenged elector.
Wis. Admin. Code Elections Commission EL 9.04