Answer

So we need to identify the nouns in the sentence. 

What are nouns? 

Naming words... The name can be of anything-human beings, mountains, rivers, name of qualities-like patience, courage etc

What are the naming words here? 

Alisha-name of a person

Biscuits-name of a food

Milk-name of a food

So we got 3 nouns in the above sentence.