Can anyone tell me how can we use Kendo UI in D365 FO forms?
It depends on what exactly you want to achieve, which you unfortunately didn't mention.
I doubt you can use it for F&O controls. It could be used by Microsoft, but you're not the one who builds the UI framework. The most advanced thing you can do it building extensible controls that are used inside the UI framework defined by Microsoft.
But you could also use an iframe and do whatever you want there.
Thanks. Is there any extensible controls of graphical representation(like Process flows) which can be used in D365 FO Forms.
What do you mean by that?