According to John, the people wanted to know if Jesus was the special person sent by God, called the Christ. They asked Him to tell them clearly so they wouldn't be unsure anymore.
John 10:24: Then came the Jews round about him, and said unto him, How long dost thou make us to doubt? If thou be the Christ, tell us plainly. [make...: or, hold us in suspense]
This verse immediately contradicts John 10:24 by stating that Jesus had already told them plainly, addressing their demand for clarity.
John 10:25: Jesus answered them, I told you, and ye believed not: the works that I do in my Father's name, they bear witness of me.