If you're talking about finding which particular textures (.mat files) were used in the levels, there's currently no program to do that.
ConMan can extract the textures from the gob/goo files (you'll have to find which container it's in), and Mat16/MatMaster/JKPaint can edit the textures. Z/Jed of course can preview the textures in the various containers.
JKPlus (if I recall) just changes all the textures in the containers to try to make them look better, but that's just it -- it's just a unique type of mod, in a way.
Hope something here answers your question.