This is an unappropriate question and it cannot be done. Whenever your Sim changes clothes or takes a shower a curtain encloses them so you can't see them. Besides even if you go close up when...
there is a cheat for it and it is nudity_forcastawaypc and if your wondering how you get the cheat box up you press ctrl - shift - c at the same time and if it doesn't let you bring the cheat box,...
You first have to unlock the Costume Trunk. After that, buy it and place it somewhere. Have your Sim go over to it, and select the one about nakedness (I forgot what it had said, though).
Then your...