how do I get latest itunes version on ipad mini?

There is no iTunes for iOS/iDevices.

There is an iTunes music/video purchase store app and the Music app for Apple Music and your own iTunes music library from iTunes on a computer.

What iPad Mini model do you have are what, exactly, are you looking to do on that iPad Mini?

You download latest version of iTunes on your PC, go from there. https://support.apple.com/en-us/HT201352