Really depends on where you are. When we lived in Minnesota, the knowledge test was the same for 2 or 3 wheels, but if you took the skills test on a trike or a sidecar rig they noted on your license that you were limited to 3 wheels.
We moved to Arkansas, Gloria took the skills test on her trike and she got a regular motorcycle license.
There are some states that require a motorcycle license to pilot a trike, but they don't have a provision to take the skills test an anything but a 2 wheeler. Connecticut is like that. I remember John Luciano was working on a bill to allow folks to take the test on a trike and have a 3 wheel restriction on the motorcycle lecense.
Now for the short answer

- check your local license testing office, whatever that is in your state.