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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.
“It is difficult to get a man to understand something, when his salary depends on his not understanding it.”
― by Upton Sinclair, who helped clean up the meat packing industry and other factories