 There is one occasion in John 10, 24, where it says the Jews were saying to Jesus, how long will you keep us in suspense? If you are the Christ, tell us plainly. But that wasn't honest doubt. That wasn't a struggling to believe. They were fixed in their hatred and unbelief. That was just their unbelief trying to put Jesus on the spot. Every true expression of doubt in the four gospels relates to believers.