I'm sorry if these questions seem trivial, but it would help me understand the UAF architecture better.
You can test your client with FIDO UAF Conformance Testing tools (https://fidoalliance.org/certification/conformance/), you need to register first. You can also test with your own server, eBay has an open source UAF server on Github.
I think the server will not know if an UAF client was installed unless the client sends an UAF request, however your client needs to match the policy within the UAF request. The communication between server and client is through HTTP. If you talked about the communication between client and authenticator, then you have implement ASM API