I see the Open TLD "mobi" supports DNSsec, but even with the site registered via GoDaddy and with custom name servers, GoDaddy does not show an option for DNSSec like it does for other DNSSec enabled domains (com, etc).
So I gather its not supported as yet, so this is more of a question on when it will be supported?
You can view a list of the domain extensions that currently offer the DNSSEC option here: https://www.godaddy.com/help/dnssec-faq-6135?. We're always working on adding new options for customers, so .MOBI may be available in future, however I do not have any time frame to provide for updates. I have passed along your request through the proper channels for consideration. Thank you.