If you need to determine which of your contacts have email addresses entered on their CRM records, you can go to your Advanced Search page and set your search up as in the below example:
Basically, this will return all contacts within your database that have an @ sign somewhere within their Email field(s). Note: this won't guarantee that your entered email addresses are accurate, but only that you've entered something which is likely to be an email address for them.
If you need to determine which of your contacts do not have an email address on their record, you can run the below search:
If you would like this data in Excel format, once your results are returned for either of these searches, click your Contact Options menu and choose "Exports". Next, choose "Email Addresses" in the resulting dialog — you can then open up the resulting Excel file after it has downloaded.