just want to know how acidic to make my solution to salt dmt out of naphtha

Well since it works with vinegar (5% acetic acid which is a weak acid) I think it suffices if the pH is below 4.
But really you could use any diluted acids, HCl, H2SO4, HNO3 in the range of 0.5 - 2N should be all good.
I wouldn't mess around with mixtures of those three in concentrated solutions since that will fuck up nearly every organic molecule.