JR Tokyo Wide Pass on N'EX

Can I use JR Tokyo wide pass travel from Tokyo Station to Kawaguchiko Station on N'EX train?

Yes

The N'EX does not go all the way to Kawaguchiko on all days. You may have to take train to Shinjuku, transfer to Chuo line, and again transfer to Fujikyu Railway at Otsuki.

For more information, check the Tokyo Wide Pass webpage on the JR East website.

in fact, i am planning to buy the JR tokyo wide pass for travelling to GALA. Then return from Gala to Tokyo stationon 3rd day. My next destination is Mt Fuji on the same day. From Tokyo station, I found that N'EX provide one trip to Kawaguchiko Station on Saturday and Sunday. Not sure whether this route cover by the JR Tokkyo Wide Pass or not.

Anyway, thanks for your answer.

That Pass covered until Kawaguchiko and by N'EX.
http://www.jreast.co.jp/e/tokyowidepass/
But N'EX for Kawaguchiko operate numbers not so many
and via Shinagawa detour route not so fast
and tranfering at Tokyo farest walk distance long very inconvenient.
http://www.jreast.co.jp/e/stations/e1039.html

See this rail map first.
http://i.imgur.com/1fEaFFx.jpg
(NEX is Red box route via "Shinagawa" some colored box is not stop stn)

Best way :
Shinkansen get off at Omiya
then take Shonan-Shinjuku line rapid until Shinjuku (brawn box route)
http://www.jreast.co.jp/e/stations/e350.html
then take Chuo main line LtdExp Super Azusa/Azusa/Kaiji until Otsuki (purple box route)
http://www.jreast.co.jp/e/stations/e866.html
finally take Fujikyu Railway(not JR) train until Kawaguchiko.

2nd :
Shinkansen get off at Takasaki
then take Hachiko line local until Hachioji (light green box route)
http://www.jreast.co.jp/e/stations/e934.html
then take Chuo main line LtdExp Super Azusa/Azusa/Kaiji until Otsuki (purple box route)
http://www.jreast.co.jp/e/stations/e1227.html
finally take Fujikyu Railway(not JR) train until Kawaguchiko.

But this route is shortest distance
but JR Hachiko line train operate numbers not enough.
If matched need more than transfering but time may faster.

3rd :
Shinkansen get off end stn Tokyo
then take Chuo line rapid until Shinjuku (orange box route)
then take Chuo main line LtdExp Super Azusa/Azusa/Kaiji until Otsuki (purple box route)
finally take Fujikyu Railway(not JR) train until Kawaguchiko.

This route train numbers enough but worthless
as total time and tranfering at Tokyo a bit long aslo inconvenient.
But some Azusa/Kaiji in early evening and night dep fr Tokyo(orange box route).

Use HyperDia fr Takasaki. (Gala Yuzawa is seasonal stn data update yet)
This is Gala Yuzawa stn timetable (JR-East official)
http://www.jreast-timetable.jp/1611/timetable/tt0408/0408011.html
(click each dep time)
http://train.gomi.info/images/naganoshinkansen/eki-name-takasaki-s.JPG
(random search) https://goo.gl/eeSo5j