There's a few ways to get this information depending on your configuration.
1) As already mentioned, if you have SSH access to your ESXi host, you can login and run the following command:
openssl x509 -in /etc/vmware/ssl/rui.crt -fingerprint -sha1 -noout
2) You can also get this "remotely" by connecting to the host (no creds required) to get the cert and to get the thumbprint using openssl, this of course assumes your host is on the network and reachable:
echo "" | openssl s_client -connect 172.30.0.252:443 > /tmp/cert
openssl x509 -in /tmp/cert -fingerprint -sha1 -noout
3) If the hosts are already connected to vCenter, you can easily obtain the thumbprint by just going to vCenter using a script querying the vSphere API