Remember that the NGX was developped for a 32bit environment... Some features may have been left out for that reason. 

But nevertheless you still can programm the point on the LEGS page and then add this LL01 or whatever it's called to your FIX page.

On 2/13/2018 at 4:09 PM, Attilio said:

Flying in areas with famous mountains (St Helen, Everest, K2 ....) I would like to see the point on my ND.
So I should add a waypoint on the NAVDATA with certain coordinates and then insert this waypoint on the fix page.
How can I do?

On the CDU you would press INIT REF, LSK 6L and select NAV DATA at 1R.  If you enter a fix on the NAV DATA page that does not exist in the database boxes will appear allowing you to define a custom airport, NAV aid or fix.  You can then use that new fix as you would any other in the route, legs or fix page.

this is how it works in the airplane anyway, I haven’t tried it in the NGX.

I guess he is trying to make these custom waypoints which are doable in the real fmc, but not the ngx fmc.

If my memory serves correctly, 100 custom waypoints can exist at any one time and get deleted/dumped when the flight is completed.

Note the ability at the end which I’m not sure the ngx is capable of.