Where do I find the tables that a role has access to in Vertica?
SELECT * FROM grants ORDER BY grantor, grantee;


The privileges_description column shows the privilege types, such as (in your case) SELECT.  (If you only want the SELECTs, you can refine that query.)

Source: Viewing Privileges Granted on Objects in the Admin Guide.  (That's from the documentation for version 7.1.x.)