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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.
“We need randomness, mess, adventures, uncertainty, self-discovery, near-traumatic episodes, all those things that make life worth living; compared to the structured, fake, and ineffective life of an empty-suit corporate leader with a preset schedule.” From Dr Nassim Nicholas Taleb, Antifragile: Things That Gain from Disorder