It does not have any knocking issue. Only few vitz 1.0 have knocking issue. I have 1.0 and i dont use high octane.. only once in a month when there is reserve light on, i add high octane of 1000rs and then again at the reserve, tank full with normal petrol.
1.3, if in good condition is soundless and no knocking. It has 4 cylinders and cng can be installed on it but i wouldn't suggest you to buy a vitz if you are planning to run it on cng doesn't matter if its 1.0, 1.3 or 1.5. Buy a 2006 onwards honda city for that purpose.