What the meaning of overhead expenses & where I have to register the auditing expenses?

As a sort of very generic definition, overhead is indirect expenses, i.e. those that aren't directly related to what you do for your business. For manufacturing, there's a more specific definition. For a service company, it gets a little hazy and a lot of opinion is involved, so it's not clear-cut.

I'm not sure how that's related to the auditing expense, except whether you're asking if that's overhead. I'd say yes, because it's related to the administrative expense of keeping your financial records (whether you mean an accounting audit, tax audit, or whatever).