You can find the handles of custom characteristics, characteristic declarations, and descriptors in the BLE_custom.h file under Generated Source. You can use the macros of the handles defined in this file.
Coming to the UART_BLE_Central example, the format of the find information response was known to the code developer. When the find information response returns 0x2902(CCCD) on byte 3 and 2, the lower two bytes(byte 1 and 0) would return the handle of the CCCD.
In the above case, we are trying to determine the handle of an attribute on the server. In your case, since you are the server, you can find the handles directly in the BLE_custom.h.
Hope this helps! Have a great day.
I think so you missundertood me, I am working with a central not with a server. I understood how work now with your explanation, but what happend if I´ve more than one CCCD?