I have used the service desk procedure step called WriteScriptLogEntry().
Where can I find the output of this step?
This will write to the "Agent Procedure Log" (slightly confusingly).
You can see this log in 3 places
1. Agent Tab -> Agent Logs. Select the machine and select the "Agent Procedure Log"
2. Hover over the agent icon until the Quick View window appears. You can the select the Agent Procedure Log there
3. Hover over the agent icon, select "Live Connect". When that page loads, you can go to the Agent Data tab and again, select the Agent Procedure Log there