What should be the type of practice does an amatuer design engineer need to do for facing an interview ?
What types of models are generally asked , which commands should be practiced for assembly purpose?
I think it really depends on the company you are interviewing at. You'll need to know what they produce, and practice those types of models.
You can show them a portfolio of other/different designs to show off your skills.
A company making sheet metal enclosures may not have a lot of use for someone who is really great at making models of cars.