Some versions of Fruit Ninja VR have extra blades, see more details below. Once you unlock a blade the Blade Stand will become available. You can change blades here by using the Trigger buttons on your controller.

There are no different dojos yet.

There's the Halloween Blade (prize only, no longer available), Christmas Blade (awarded automatically when playing the first game) and Pineapple Blade (awarded when completing the Pineapple Express achievement)

Pineapple Blade (awarded when completing the Pineapple Express achievement)

Pineapple Blade (awarded when completing the Pineapple Express achievement)

At the moment you can’t. However, the team is hard at work on bringing you these features.