API reference come with the installation package. Once you have APIC-EM running you can access reference doc form UI.
You can also view the reference doc from DevNet
I am searching for a python SDK, so I don't have to deal with the REST API. On Cisco Live in Milano I heard this should be already available. Can anybody confirm that and provide that code?
There is a pyhton SDK for APIC but I am not aware of any for APIC-EM. If I hear more I will post it here.