34 The crowd spoke up, “We have heard from the Law that the Messiah will remain forever, so how can you say, ‘The Son of Man must be lifted up’? Who is this ‘Son of Man’?”

Read John 12:34 Using Other Translations

The people answered him, We have heard out of the law that Christ abideth for ever: and how sayest thou,The Son of man must be lifted up? who is this Son of man?
So the crowd answered him, "We have heard from the Law that the Christ remains forever. How can you say that the Son of Man must be lifted up? Who is this Son of Man?"
The crowd responded, “We understood from Scripture that the Messiah would live forever. How can you say the Son of Man will die? Just who is this Son of Man, anyway?”