Learn Italian: L'assaggiatore bendato non sa quello che mangia. - The blindfolded taster does not know what he is eating.

In this sentence, sapere is used in its standard sense of knowing a fact or piece of information. The sensory meaning (to taste of or smell of) strictly requires the preposition di immediately after the verb, as in sa di fragola (it tastes like strawberry). Without di, it simply means "knows".

Why use quello che for "what" instead of just cosa?

While you can say non sa cosa mangia in modern Italian, quello che (literally "that which") is extremely common and natural for expressing "the thing that" or "what" in statements. You could also use ciò che as a slightly more formal alternative.

Where does the word bendato come from?

Bendato means "blindfolded". It is the past participle of the verb bendare (to bandage or blindfold), which itself comes from the noun la benda (bandage or blindfold).

What exactly does an assaggiatore do compared to someone who just eats?

An assaggiatore is a professional or dedicated "taster". It comes from the verb assaggiare, which means to taste or sample a small amount of food or drink to judge its flavor, unlike mangiare which is just the general act of eating.