The online programs write to the CSMT/CSSL logs. Where do these logs reside and how can they be accessed?

On the mainframe, CSMT is redirected to CSSL, which is an extra-partition queue associated with a DD named MSGUSR. By default, we define CSSL as intra-partition, so you would need to write a program to retrieve the messages and write them out to the DD statement of your choice.
BR>There is a sample attached to this article that will put a trigger on the CSMT queue, so any messages written there will be sent to console.log. If the destination needs to be changed, the sample can be modified. README file attached documents instructions for the sample.