knx_extra.xml file are published to a DropBox folder available here: https://www.dropbox.com/sh/uwkdggd10fi1955/AAAhMkD6CoQtLx-A_DPEoguga?dl=0The latest version is always knx_extra.xml in the root of this shared Dropbox folder.
Previous Versions of knx_extra.xml sub-folder, however it should not be necessary to use these and if one were required you must rename it to remove the _vXXX suffix. knx_extra.xml from Dropbox and put it in the knx sub-folder of your
C:\Niagara\Niagara-n.n.nn\knx\knx_extra.xml).
Knx Data Defs followed by clicking the .
Imported Files.
knx_extra.xml file you copied into the knx sub-folder of your installation and displays: 
If you clicked Imported Files, the Ets Project File Import Manager view opens. Otherwise the focus remains on the AX Property Sheet.

Knx Data Defs.