Get patch status of all RAC instances
It will list the node names where the SQL patch is not applied.

SELECT dbms_qopatch.get_pending_activity FROM dual;
OR
SELECT xmltransform(dbms_qopatch.get_pending_activity, dbms_qopatch.get_opatch_xslt) FROM dual;

Compare the node/instance for patch applied in RAC

dbms_qopatch.opatch_compare_nodes(
node IN VARCHAR2 DEFAULT NULL,
inst IN VARCHAR2 DEFAULT NULL)
RETURN VARCHAR2;

Set the instance at database level for further inventory commands:
Sets the node name and instance to get the inventory details specific to it in an Oracle Real Application Clusters (RAC)
environment

dbms_qopatch.set_current_opinst(node_name IN VARCHAR2 DEFAULT NULL, inst_name IN VARCHAR2 DEFAULT NULL);
Example:
exec dbms_qopatch.set_current_opinst(inst_name=>'rac1');

select xmltransform(dbms_qopatch.get_opatch_bugs, dbms_qopatch.get_opatch_xslt) from dual;
  Bugs fixed:
          19157754  18885870  19303936  19708632  19371175  18618122  19329654
19075256  19074147  19044962  19289642  19068610  18988834  19028800  19561643
.............

Querying from SQL patch registry to produce complete patch level information

Set serveroutput on
exec dbms_qopatch.get_sqlpatch_status;