From [wikia](http://hunterxhunter.wikia.com/wiki/Alluka_Zoldyck) : 

>According to Killua, the degree of wish that Nanika can grant is probably infinite

Killua ask her to "turn gon back to normal" so Nanika saved Gon turn him back to a "normal" kid, he nen is closed now. Ging say this to Gon in the chapter 345.

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/iZS3X.jpg