I'm not sure that this really makes it more clear. what code were you putting where?
the function that takes read is the reader

Based on how I read it I was trying many variations of:

return function (read) {
     if (end) return cb()
       console.log(data)
       read(null, next)
    read(null, function next (end, data) {
 })

...because the line that I have now moved down seemed to suggest that the function was supposed to be above (i.e. in the place where the comment was)

what do you think you would have done if there had been no comment,
or it was more incomplete like

return function (read) {
    read(null, ...)
 })

you must have gotten lots of errors about data and end and cb being undefined