My feeling is that Kob will take almost anything most of the time (bloodworm, prawn, fillet, livies tjokka etc.)
I think the bigger trick is to be at the right place at the right time for Kob - they come and go and even the right water temp and colour can never guarantee a kob.
If I'm specifically targeting Kob, my bait of preference is Okkie leg - not because I think he prefers this, but because a live bait or fillet is more likely to attract a shark before it attracts a Kob. This is definitely the case for my location.