Hello,
to be able to point you into the right direction, I think you need to be a bit more specific.
You can have a look into the API Explorer under Journal Entry (JRNLE) for possible fields.
Another approach could be to use the Search module in Fusion and map the Outputs to * to get an idea of how the journal entries, which represent the system activity, are structured.
Afterwards you can setup the Search module to search for journal entries containing your search string in the field you have determined.
Regards
Lars