How to remove water stain from camera of Sony Xperia Z2?

Usually, a simple wipe using a microfiber cloth should work. If you have a family member or friend that has eyeglass cleaner, borrow it to clean your camera cover.

Can I recover a video from the formatted hard disk of Sony Xperia Z2?

You mean record a video after the phone was formatted? Yep, no problems.

How many pixels does the camera of Sony Xperia Z2 have?

The rear camera has 20.7 MP while the front cam has 2.2 MP. Find out more about the specs from the Sony Xperia Z2 page.

Where can I get replacement screen for the Sony Xperia Z2?

Doesn't matter if it's under warranty or not, cause if the reason for screen replacement is not factory defect, then you won't get a screen replacement for free. What you can do is contact Sony and ask for a quote. Then I also suggest that you go to nearby cellphone repair shop and ask for a quote too. This way, you will have options to replace the screen. Best option is repair from Sony but may cost more than other cellphone repair shops may offer.

Where can I get help if the Sony Xperia Z2 fail the waterproof test?

I suggest taking it to an authorized Sony service center or to the store where you bought. Contact Sony to locate the nearest service center in your place. Good luck!

Is it true that if you damage your Sony Xperia Z2, you can buy a new one half the price?

Hmm.. This is something I haven't heard of. I suggest that you contact Sony and/or the store where you bought it. Let me know how it goes.

Will Sony replace the screen of the Sony Xperia Z2?

I'm sorry to hear that. Of course they will, but they will charge you. I'm not sure exactly how much, but basing on the prices here in my country, it would cost not more than $100. I suggest contacting Sony to be sure about this. Good luck. Hope you get your phone fixed soon.