Yes you can but you can not test the surface for example you can touch the green to regain balance you can touch the green to remove debris etc. But you can not "rub" the green to test the surface condition.
Yes, your knee can touch the ground as you stand (or kneel) behind the ball to line up a putt. What "can't" be done by a caddie or golfer is touch the ground along the intended line of a putt.
"Action Putting Greens" has a website at www.actiongreens.com. They sell many artificial-style greens and offer free samples before you buy.
to touch a touch
Real estate prices always vary by location, hence, there is no standard price for a putting green.
There are several options available when you wish to purchase a portable putting green. Locally, The Home Depot sells indoor practice putting greens. Online you can purchase an indoor putting green from Amazon or eBay. For a large green, a specialty company such as Putters Edge can be contacted.
It will at some point rest against the pin! Regardless of that, if you putt with the pin in, and the ball is holed, you receive a two shot penalty. The scenario set out in the question means nothing.