The discovery endpoint can be used to retrieve metadata about your IdentityServer - it returns information like the issuer name, key material, supported scopes etc.
The discovery endpoint is available via /.well-known/openid-configuration relative to the base address, e.g.:
https://demo.identityserver.io/.well-known/openid-configuration
You can use the IdentityModel client library to programmatically interact with the protocol endpoint from .NET code.
var client = new HttpClient();
var disco = await client.GetDiscoveryDocumentAsync("https://demo.duendesoftware.com");