Do
/help debug, it will print
/debug <start|stop|chunk> [<x> <y> <z>]. This syntax implies that a set of coordinates can always be supplied, but coordinates should only be supplied for chunk mode, which I believe has been removed, so that argument should be removed from the help text as well.
Comments 2
When I made this bug report, I checked if
/debug chunk 1 1 1did anything, but all that happened was it printed the usage text in chat, so it is probably removed. They probably forgot to update the usage text after it was removed, after all they forgot removing it for a snapshot release as well, source: http://www.reddit.com/r/Minecraft/comments/2c5f35/minecraft_snapshot_14w31a_has_been_released/cjct3k1?context=1
So /chunkinfo might be one of those disabled/removed commands as well.
Correct syntax would be
I don't think that the chunk-debug mode was removed since this command was recently updated for translation at crowdin.com and there is a new (but unavailable) command
See https://crowdin.com/translate/minecraft/9380/enus-de#5154167