Use the verify option to verify certificates.
openssl verify cert.pem
If your local OpenSSL installation recognizes the certificate or its signing authority and everything else (dates, signing chain, etc.) checks out, you’ll get a simple OK message.
$ openssl verify remote.site.pem remote.site.pem: OK
For this to work openssl needs to have access to the CA that issued the certificate. Otherwise you will get an error like:
error 2 at 1 depth lookup:unable to get issuer certificate
To import CA certificates see here: Import CA certificates for openssl to use