The discovery endpoint can be used to retrieve metadata about your IdentityServer - it returns information like the issuer name, key material, supported scopes etc. See the spec for more details.
The discovery endpoint is available via /.well-known/openid-configuration relative to the base address, for example if your base address is ‘https://demo.identityserver.com’:
https://demo.identityserver.com/.well-known/openid-configuration