You can generate a fingerprint for a public key using ssh-keygen like so
ssh-keygen -lf /path/to/key.pub
Concrete example (if you use an RSA public key):
$ ssh-keygen -lf ~/.ssh/id_rsa.pub 2048 00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff /Users/username/.ssh/id_rsa