Today I have the practical interview of xamarinForm

As per the fresher you can prepare for these programs to workout :

How to display alert in Xamarin.Forms?

How to draw rectangle in Xamarin.Forms?

What is difference between Margin & Padding property?

What is difference between DisplayAlert and DisplayActionSheet?

How to use Device.OnPlatform in xaml and C#?

How to make View-to-View Data Binding in Xamarin.Forms with Xaml?

How to increase rows & columns space of Grid in Xamarin.Forms?

Regarding ReactiveUI

Read this link : http://www.ezdev.org/view/xamarin/6693