"Do you like this fish sauce?"
Translation:Placetne vobis hoc garum?
But if there's only one person, I think the person know it's a singular you. Thank you for your useful answer.
Yes, I wanted to say, for people who have a doubt. Here both are valid:
Placetne vobis hoc garum? (vos->vobis, plural)
Placetne tibi hoc garum? (tu->tibi, sing.)
The verb doesn't change from "placet" (sing) to placent" (plural) if you use a plural you, as the subject of the verb is "garum".
Haec gara placent tibi/vobis: plural.
I don't think it is acceptable, because what you put says, "This fish sauce is pleasing to you?" which is a statement, and although in English it askes for confirmation, it does not do the same thing in Latin. The -ne is required for a yes or no question. In English we usually make it a question by switching the word order, "Is this fish sauce pleasing to you?" but in Latin word order has minimal usage and so an ending is required, thus the suffix -ne.
When phrasing a question in Latin the verb is put at the beginning with a -ne enclitic particle attached to the end of the verb. So it should be the first word in the sentence. Only in questions is the word order very strict. Although Latin follows SOV order most of the time, word order does not contribute to meaning directly, only to emphasis.