Learn Danish: Drengen har tre gode spørgsmål. - The boy has three good questions.

In Danish, many short nouns that are neuter (they take et in the singular, like et spørgsmål) do not change their form when they become plural. Because of this zero-ending rule, both 'a question' and 'questions' are simply spørgsmål.

Why is the adjective good spelled as gode with an e on the end?

Adjectives in Danish change to match the noun they describe. When an adjective describes a plural noun, like 'three questions' here, you must add an e to the end of the base adjective. So god becomes gode.

How do we know Drengen means 'the boy' instead of just 'a boy'?

Danish puts the word for 'the' at the end of the noun as a suffix. The base word is dreng (boy), which is a common-gender noun (an en word). To say 'the boy', you attach that en to the end, making it drengen.

If spørgsmål is exactly the same in singular and plural, how would I say 'the questions'?

Even though the basic plural doesn't have a special ending, the definite plural (meaning 'the' plural items) still gets one! You add -ene to the end. So 'the questions' would be spørgsmålene.