How to make a print screen on iPad Air 2 ?

Briefly press the on/off and home buttons together. You should hear a clicking sound like a camera taking a photo.

This action will place a screen shot on your iPad's Camera Roll. You can then treat this as you would any other photo.

If I so this on my iOS10 ipadair2 always Siri opens. What to do?

That implies that you are pressing and holding the home button for too long - if you press and hold the on/off (aka sleep/wake button) and then briefly click the home button (and then release the on/off button) you should get a screenshot