How can we enable Einstein Analytics in salesforce org? Do we need to purchase license? Can we enable Einstien Analytics in developer org?
You can enable Einstein Analytics in a scratch org (as opposed to a dev org) by setting features in your scratch org definition file.
Einstein-related features you can turn on include
It looks like
DevelopmentWave is probably the core feature you want:
Enables Einstein Analytics development in a scratch org. It assigns five platform licenses and five EA platform licenses to the org, along with assigning the permission set license to the admin user. It also enables the Analytics Templates and Einstein Discovery features.