Gmail(google) password
You can reset the password using Google password recovery. Go here - Account recovery.
Follow on-screen instructions:


Select I don't know my password. Type your email address.
It asks for any previous password you remember (if there is one). Type password &amp; continue.
Next screen will be like this - Confirm password reset on my Android XXYYZZ phone. Select Send Notification.
Follow on-screen instructions afterwards.  


Edit 1:


If you don't have access to your mobile device and do not have an alternate email ID, you can still recover/reset password by answering some questions on recovery page. You need to follow on-screen instructions carefully to reach that page.