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 1, Email 2 or Email 3 fields. 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 first run a search to bring up all contacts within your database.
Once your results are returned, from the Exports menu in your Advanced Search Result Options widget choose "Email Addresses (XLS)" — you can then open up the resulting Excel file. From there, you can scroll down through all the contacts to quickly see which ones are missing Email Addresses on their records. Or, you can run a Data Sort within the file to group all those without an Email Address together.