Maybe you just read the text file that given with the wad?
nicolas patrois : pts noir asocial
Signature
GLOU-GLOU
P : Ouerk ! C'est dégueulasse, j'ai bu la tasse ! M : Panique pas... La mer est pleine de microbes, mais tellement dilués qu'ils sont inoffensifs... P : C'est ça... La mer, c'est de la merde homéopathique !
You can find text MAPxx or ExMx near the end of the wad file. Or you can open it with one of the front-ends that scan the wad and tell you what maps are inthere.
Hmm, maybe (at least in the old DOS days) when the game starts? If with a newer front end, maybe look for an "about" menu selection under the help menu?