I'm pretty sure by 2010 Cadillac was using an integrated relay for the horn.  It's soldered onto the printed circuit board inside your fuse box and is "non serviceable".

So if that's the case how can you troubleshoot what's going on here?

First, if your key fob has a horn button, press it. If the horn still doesn't work then it's probably not an issue inside the steering wheel or the steering column ground.

If the horn does work then it probably is.

If the fob can't sound the horn then check the test tabs (on that horn fuse you just checked) for power on both tabs. Use a test light. That's probably a 15 amp fuse and it's protecting the Load Side of that relay and the wiring to the horn.

If you have power there then disconnect the electrical wiring connector at the horn and use some wire to jump power and ground to the horn.

If the horn doesn't work, your horn is dead, Get a new one.

If the horn does work then test that connector that you just unplugged from the horn to make sure it's getting power and ground to the horn when the horn is being activated by either the key fob or the horn pad on the steering wheel.

If it isn't, inspect the connector for corrosion and the wiring for damage. The horn, its connector, and wiring, are usually down low and right up front and they're exposed to road salts, water intrusion, and general crud. They take a beating.

This stuff is unnecessarily complicated these days. Why a control module or an integrated power module is involved in sounding the horn is beyond me. I guess people just like tooting their horn with a key fob from 30 feet away, or having it sounding because of it being "theft" triggered (which no one pays attention to anymore)

If you're going to be doing your own work, then you need a manual.

These are worth every penny.