The function of the word dónde/donde indicates if it does or does not require a written accent. Even though the most natural translation for both is "where", it can help you to remember that if when you translate the phrase into English you can replace "where" with "in what location/to what location"; then you know it is dónde with the written accent. Look at these examples:
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Adonde is an adverb of place that indicates movement or destination. We generally use it with the verb ir (to go) or any other verb of movement. Adonde is usually translated into English as where [to].
Both adónde and adonde indicate some movement or a destination, and can generally be translated into English by including to along with where. Adónde is a question word, while adonde is used in statements.