cluster A NIfi & Registry are managed by Ranger, working well.
hence I added cluster B nifi node cert to cluster A Ranger user and then added to Registry policy.
clusterB nifi user logs:
2020-08-04 21:40:37,824 INFO [NiFi Web Server-333] o.a.n.w.s.NiFiAuthenticationFilter Authentication success for divya 2020-08-04 21:40:37,833 INFO [NiFi Web Server-333] o.a.n.w.a.config.NiFiCoreExceptionMapper org.apache.nifi.web.NiFiCoreException: Unable to obtain listing of buckets: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors. Returning Conflict response.