As a Christian, I would say nothing, but listen prayerfully with the scriptures in mind. Depending on the guidance and leading of the Holy Spirit in me and whether any scriptures were violated, I might ask the voice some key questions concerning Jesus Christ, like is he the son of God come in human flesh and did he raise bodily from the grave. The NT says any spirit that denies who Jesus is is of antichrist. If the answer is scriptural I would then likely worshipfully fall on my knees and listen for what God has come in such a manner for.
If in my mind I would determine that scripture was being violated and I decide that this is an evil spirit, I would then rebuke the spirit in the name of Jesus.
I would not necessarily ask for any miracle, for Satan's demons are powerful miracle workers also, and pose as "angels of light."