Good evening,
There are several things that this "bump' could be. Anything from a wart to a bug bite. The only way to know is to have it examined by your vet. I am sending you a link that discusses the types of "unusual bumps" that dogs can get, their diagnosis and treatment options. It will give you a very good place to begin and things you can discuss with your vet.
http://www.peteducation.com/article.cfm?cls=2&cat=1593&articleid=424
I hope this helps. Please let me know if you need further information.
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