Wis. Stat. § 6.925
Any elector may challenge for cause any person offering to vote whom the elector knows or suspects is not a qualified elector. If a person is challenged as unqualified by an elector, one of the inspectors may administer the oath or affirmation to the challenged elector under s. 6.92 and ask the challenged elector the questions under that section which are appropriate to test the elector's qualifications. In addition, one of the inspectors shall administer the following oath or affirmation to the challenging elector: "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 then ask questions which are appropriate as determined by the commission, by rule, to test the qualifications of the challenged elector.
Wis. Stat. § 6.925