There’s an unofficial site that allows you to search to see if your email address was in the AshleyMadison data dump. I’m providing the link to the site without any warranty as to its accuracy or legitimacy: https://ashley.cynic.al. The site cannot check for wildcards; you need to enter a specific email address.
NOTE: Even if you do find an email address in the data dump, do NOT assume that the person associated with the email address was a member or user of the site. AM did not verify email addresses, so anyone could sign up using any email address.
And if you find your own email address in the data dump and know that you never signed up, well, I’m not sure what to advise you as to how to address that.