We recently overhauled our ISE deployment and had to import everything from the old ISE servers into the new environment.
Since we were exporting from and importing to ISE it was quite easy, just exported what we wanted (network devices, devices in static groups, etc.) and then just use the import function in ISE to bring them over.
If you are starting from scratch or importing from a different platform it is more work, luckily ISE has templates you can use to make it easier. For endpoints if you go to Context Visibility > Endpoints there is an option to import, when you choose Import from file there is a link to Generate a Template. It is similar with network devices too, Administration > Network Devices > Import > Generate a Template
Just follow the format of the templates, just leave any unnecessary information blank. It might also be helpful to put a couple of test devices/endpoints into ISE and export them to get an idea of the required information. Hopefully this gives you a place to start when importing your objects into ISE.
