Learn Croatian: Je li škola blizu?

In Croatian, yes/no questions are often formed by taking the verb (here, je meaning "is") and adding the question word li. You cannot just use Je by itself to start a question like you do in English.

How would I answer this question negatively using the words from this lesson?

You would use the negative form of je, which is nije. To say "No, it is not," you just say Ne, nije. For the full sentence "The school is not near," you would say Škola nije blizu.

How would I ask the negative version, "Isn't the school near?"

You simply replace Je with its negative form Nije. The question becomes Nije li škola blizu?

Does blizu change its ending because škola is a feminine word?

No, blizu is an adverb (a word that describes where, when, or how something happens). Unlike adjectives, adverbs do not change their endings to match gender or number. It always stays blizu.