From here https://www.igorkromin.net/index.php/2016/05/27/how-to-get-orapki-without-installing-the-full-fusion-middleware/

Ok, this is an annoying process

First download jdeveloper (maybe the smaller one Oracle JDeveloper Java Edition 12.2.1.4.0)

https://www.igorkromin.net/index.php/2016/05/27/how-to-get-orapki-without-installing-the-full-fusion-middleware/

https://www.oracle.com/tools/downloads/jdeveloper-12c-downloads.html

Nope, download the gigantic one (studio)

The java downloader is a bit finicky, wait until it really says complete for both files

Ok, this is totally daft, rename V998594-01.zip to V998593-01-2.zip

Right click run as Administrator on the .exe!

After it is done installing (takes forever)

Find orapki at

 Windows

C:\Oracle\Middleware\Oracle_Home\oracle_common\bin\orapki.bat