It's easy: Manzanilla comes from Sanlucar de barrameda, so you want to find one with that D.O.. The Manzanilla is a fortified wine (as are all Sherries) & I'm not sure if such wines have a D.O.
Just buy one from Sanlucar and drink it very cold (w/mejillones or boquerones or a similar tapa). In Madrid, VillaRosa on Plaza Santa Ana used to have it from the Baril, the best Manzanilla I have tried.