Assalam alaykum wa rahmat Allah wa barakatuh.
Is it necessary to make wudu after taking a bath, even if I am naked in the bathroom?
Wa alaykum assalam wa rahmat Allah wa barakatuh.
No, if you perform a ritual bath (ghusl), you have entered the state of ritual purity and thus no longer need a separate ablution (wudu) in order to pray.
You shouldn’t remain completely undressed unnecessarily, but if you did for some reason, it wouldn’t affect your ritual purity because no filth exited from your body.
Please also see: http://seekershub.org/ans-blog/2010/08/25/the-ritual-bath-ghusl-obligatory-recommended-and-disliked-acts/
And Allah Most High knows best.