Your subdomain is its unique identifier. Here are 3 ways you can find it.
Check your URL
If you have not enabled the host-mapping feature in Zendesk Support, your subdomain can be identified from its URL:
https://[ yoursubdomain ].zendesk.com
Check the Admin Home Page
If your Zendesk Support instance has host-mapping enabled, your Zendesk URL will be customized and may not include the subdomain. In that case, any administrator for your account can find your subdomain on the Admin home page . It is located in the upper right corner of the page, just below the user profile button.
In the screen capture above, the subdomain is support .
Request an Email
You can also get a list of Zendesk subdomains that your email address is associated with from this page https://www.zendesk.com/login/#loginReminder where you will presented with this prompt:
Here, type your email address and you will receive your subdomain via email.
If you have troubles receiving the email, make sure to have checked your inbox folders including Spam. Alternatively, this means that there is no account with the email address chosen.