If I remember I check DNS based RBL using a simple command:
host 12.34.56.170.bl.spamcop.com (This is a fake ip)
If the DNS returns 127.0.0.2, this host is blacklisted in Spamcop.
In Proofpoint case, the host to make this check should be: safe.dnsbl.prs.proofpoint.com
So it could be:
host 12.34.56.170.safe.dnsbl.prs.proofpoint.com
But I don't know why the proofpoint doesn't work in this way.
The difference is that the Proofpoint rbl is a paid service. You can't query it without a license.
If you are curious about a particular ip, you can look it up with this web tool:
https://support.proofpoint.com/rbl-lookup.cgi