Sometimes there could be a slight delay between the event creation and the start of the Workflow depending on the load on the system. Go back to the event log display, refresh the display (there is a refresh button), display the log for your event again. If the Workflow started correctly, you should see the workitem button.
Is event tracing switched on? Check transaction SWELS, and switch on event tracing if it is off. Then you'll see all events triggered by the system according to your selection in SWEL.
If, however, you're referring to the workflow log, that's in transaction SWI2_FREQ; this one gives you a list of all activated workflows, their status, tasks, current step, and history. I don't think you need to manually activate workflow tracing for this transaction, but I could be wrong.
Hope this helps!