There is no better Soul-R&B recording that Eddie Floyd singing Knock on Wood - it has been covered many times, but all cover versions are hoplessly inferior - why?
The reason is quite simple: the rhythm section - bass and rhythm guitars and drums (the keyboards can only be heard in the 'middle eight' from 1:46).
Eddie Floyd's singing is great, the brass section is great, the main introducing riff is one of the best ever and supplemented by a superb second riff in the verses... But it is the rhythm playing which cannot be replicated, and that is due to its syncopation.
Syncopation is the hardest thing to do well (as a broad generalisation!) - and the Stax-label house-band (aka Booker T and the MGs) that played with Eddie Floyd was a group of first rate musicians that played together A Lot.
Also they were mostly black (an exception was the genius rhythm guitarist Steve Cropper, who co-wrote and played on Knock on Wood); and most of the best players of syncopation-based music are 'American' blacks (who invented it, with ragtime - and several other forms including ska/ reggae).
This probably means that this music has become essentially un-replicable in modern times - since 'rap' displaced singing among blacks, synthesiser replaced real-instruments, and house-bands are a thing of the past...
Still, we have the recordings: what I said about Knock on Wood also applies in essence to Hold on I'm Coming, by Sam and Dave - although the vocals in KoW are another major reason why it is de facto un-replicable.
