You've already posted this in another thread, and had replies. It seems that you are looking for the answer you want to hear. That is a metallic knock at the top of the engine, possibly camshaft. It's definitely not diesel knock, and a worn injector nozzle would produce black smoke from the exhaust rather than the light grey as seen on your video. I would suggest you use a stethoscope to better identify where the noise is coming from, or remove the camshaft cover and check the camshaft and followers for wear.

Thanks for your reply,

Would camshaft knocking produce grey unburnt fuel smoke ?

Yes it could. If an inlet camshaft lobe was sufficiently worn so that a valve was not opening fully then the engine may not draw enough air on one cylinder. This would result in a loss of compression and the fuel when injected would not burn. This would explain white/grey exhaust smoke and an engine misfire.