Are you working with imported geometry (e.g. from a step or iges file)? or with native NX geometry?
If imported, try heal geometry and/or optimize face.
If native geometry, there is probably a model error that causes the face to not display properly. Run the "examine geometry" command, find the problem area, and edit the appropriate features to correct the issue.
If you are working with sheet bodies, you may want to turn on the "2 sided light" option in visualization preferences. When this is turned off, NX will not display the sheet body from the backside.
If you select one single face and then press Ctrl+I ( Information-Object)
there will be a red arrow displayed showing the positive normal of this face.
This should point out from the volume. If it points inwards, the solid is reversed.
( if you place it on a drawing and create a section view, NX might cross-section the entire sheet )
I have seen a few such reversed solids, all have been imported.
Try Heal Geometry. If that doesn't work, try split body and cut it into pieces , then it might be possible to re-unite these back into a valid solid.
If this doesn't work, you will have to extract all faces and sew these together to a valid solid.