I think the question-ness of your examples is confusing you as to whether the verb is transitive at all. "Kennen" is transitive. You always have to "kenn" SOMETHING. If your 2nd example were a declarative sentence, it would be "Du kennst den Mann", and Mann is the object of the verb kennen. The article stays "der" in your first and third examples because the verb isn't transitive at all. There isn't some subject that's tasting the salad, or naming the cheese. In fact, der Salat and der Käse ARE the subjects. Does this help?

You should always learn the complete verb pattern (cases and pronouns) together with the meaning, not just the verb. So learn "etwas (Akk) schmecken", "nach etwas (Dat) schmecken", "es schmeckt"; "etwas (Akk) kennen"; and "jemandem (Dat) etwas (Akk) geben". A good dictionary will have a number of verb patterns together with their meaning, e.g. Pons: http://de.pons.com/%C3%BCbersetzung?q=schmecken&l=deen&in=&lf= As you can see in this example, verbs can sometimes be both intransitive (and in this case, use an impersonal construction: "es") and transitive.