I have a Gmail account which I've forgotten the password now, and the SIM I used for the registration is lost. How can I retrieve my password?
You can try this option under mobile verification page...."Can't access any of these recovery options? Verify your identity by answering multiple questions about your account."
The Gmail service offers an alternative way to recover your account. Firstly, access the sign-in page and click on Need Help?. Use the options displayed on screen. When you arrive to the SMS part, choose the option with I don't have my phone. On the next page, click on Verify identity and provide the necessary items.
Verify identity page: https://www.google.com/accounts/recovery/skt