Where to Start developing XBox One Game having Kinect Capabilties

First you'll need to become an Independent developer for Microsoft assuming you aren't a business. See here: http://www.xbox.com/en-us/Developers/id this will give you access to the Unity module required to build for Xbox one.

Next, you'll need to connect your Xbox one to your machine via Internal PC to Xbox Internet connection. We haven't worked on Xbox one development yet, so we're not quite sure of the complete process of play testing, however I assume you can just play inside Unity like any other build and just select Xbox one as your platform.

1- What will be the process for beat testing & How can i allow user to test at his XBox console?

When you're near release, you can put your game on the Indie section of the Xbox Marketplace for people to download if you're going open beta, otherwise you'll have to give away codes that unlock this game for closed beta.

2- What data format Unity will return, and how to manage players data on Database? Am not entirely sure what you're trying to do? I would start with simple basics of the game and then build off it slowly. This way you know it works every time. Multiplayer games are more tough to make on any platform then they are for single player. So many things happen behind the scenes.

You can read more about the things you'll need. Best of luck!

http://www.microsoft.com/en-us/kinectforwindows/

http://www.xbox.com/en-us/Developers/id