'session specific client information' refers to specific session variables ALTER SYSTEM ALTER SESSION SET - SAP HANA SQL and System Views Reference - SAP Library.
These have to be set by the application that performs the connect to SAP HANA.
I've written about the usage of session variables a few times in the past:
SPS 6 ante portas - new features in SAP HANA Studio revision 55
This - and of course - the documentation should give you an idea on the concept.
Anyhow, the workload class mapping doesn't require you to set all of the possible mapping parameters.
If the client application doesn't fill the APPLICATION session variable, then you can assign the workload class e.g. via the user name.
Consider the following example:
create workload class lumira_user SET 'PRIORITY' = '3', 'STATEMENT MEMORY LIMIT' = '2', 'STATEMENT THREAD LIMIT' = '20';
I created a workload class for my SAP Lumira users, with a priority of 3, a statement memory limitation of 2 GB and a maximum of 20 parallel threads per statement.
CREATE WORKLOAD MAPPING "WL_LUMIRA_MAPPING" WORKLOAD CLASS "LUMIRA_USER" SET 'USER NAME' = 'OZDUDE';
Now I define that this workload class shall be assigned to connections that are made with db user "OZDUDE".
When connecting with SAP Lumira I now can see that the workload class has been assigned to the user:
select connection_id, connection_status, user_name, workload_class_name from m_connections where user_name='OZDUDE';
/* CONNECTION_ID CONNECTION_STATUS USER_NAME WORKLOAD_CLASS_NAME 207599 IDLE OZDUDE LUMIRA_USER 207597 IDLE OZDUDE LUMIRA_USER */