Re: Emmerdale
No, I don't think it's John. Whoever clobbered Cain was either the same height or a touch smaller. Whoever it was, whacked him in the legs first to bring him down, then bopped him over the head. John could have done that with Cain in a standing position.
I still don't think it's Zak because the Dingles have their own law on how to deal with their own problems, and one of them is not by violence, but more of a casting out.
Not sure about Priya. She had an axe to grind, but I'm not sure she'd have had the strength to deliver those blows, whereas Amy and Moira are a bit more buxom and would have more power in their arms to cause a serious leg injury.
Sadly, Jai compromised himself by tampering with Cain's car just at the wrong moment in time as everybody wanted a piece of Cain.