I have uploaded a website to my Compute Engine instance and I wanted to set the registrar to send the visitors to the server (Compute Engine).
Where can I get the name servers of my instance/server over Compute Engine?
Google Compute Engine does not provide a nameserver on the public internet. (It does provide a nameserver for the internal network which is private to your project, this allows you to connect to instances via their instance names rather than IP.)
If you want your instances to be available via public internet DNS nameservers, you'll need an external nameserver and one or more static IP addresses for your instances.
You have two options for static IP addresses on Compute Engine: You can have a static address for a single instance, or for the GCE Load Balancer.
See this documentation for how to configure a static IP address for an instance.
Using the Load Balancer is more flexible. See this documentation for details on Load Balancing.