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When a bike sits for a while then will not start, it is usually bad fuel, dirty spark plugs and/or a weak battery. Check those first. An engine needs 3 things to run- fuel, air, and spark. The factory service manual has procedures for checking all 3.
The knocking sound could be a major problem beginning, or something minor. I would get a mechanic familiar with this bike to listen to it and give you some advice. You could post up a video with the noise after you get it started, but this is definitely second place to having a mechanic look at the bike and doing whatever checks they think are needed.
“Do…not waste time protesting the self-inflated showmen and bloviating bullshitters who populate our culture. It’s more fun to marvel at them, to appreciate them, to be grateful for them, and to mock them relentlessly. ”-from the 2010 book American Freak Show by Willie Geist. "He wondered what difference any of it would make two hundred years from now." -from the book Cyclops by Clive Cussler.