The `/etc/ssl/certs/ca-certificates.crt` is a long text file of concatenated certificates, each in PEM format. To view details of each one, you need something like:
openssl crl2pkcs7 -nocrl -certfile /etc/ssl/certs/ca-certificates.crt | openssl pkcs7 -print_certs -noout
This creates a temporary PKCS#7 file of all the certificates in the file, then prints their subject and issuer fields only. If you want all the details, add `-text` to the 2nd command.