How do you draw white whiskers on a pencil drawn animal?

if our using only grey lead then simply draw them with a grey lead pencil but if your using colors try using white with a bit of grey or light blue

Another option is to use a small, battery powered electric eraser. They come with small nibs that are well suited to "etching out" fine lines such as whiskers.

It will take some practice, but you can etch pretty fine white lines out of a pencil drawing with these erasers and it is much more effective for the task than a kneaded eraser. If you need a super fine line, just cut the top of the eraser with a razor so that it is completely flat, giving you a nice hard edge.

Be sure and get one of the small battery powered ones. They sell them everywhere online at all the art supply stores and some office stores. These rotate faster and have finer tips than the big corded electric erasers, making them more well suited to fine detail work.