Twilight Zone horn works no fuse or relay

You're right, there is no dedicated Horn relay or fuse. What you originally circled was "S-Horn", which is unused in US market. Possibly security horn in other markets.
The horn is operated by the Integration Relay, which as it's name suggests, integrates several functions into one unit. The Integration Relay is also known as "Unit E" which resides in the Engine Room Fuse/Relay Block.
Once you disassemble the Engine Room Fuse/Relay Block, you can access the connectors for Unit E, and diagnose the circuit from there.
By the way, it would be a good idea to disconnect the 12v aux battery and take the usual precautions while working on the electrical system.

 

Just Curious, Mine is doing the same thing from a front end collision. Did you ever get this repaired? If so How?