QUICK ANSWER
"El" is a form of "el", a definite article which is often translated as "the". "Dónde" is a form of "dónde", an adverb which is often translated as "where". Learn more about the difference between "el" and "dónde" below.
el(
ehl
)A definite article is a word that identifies a noun as specific or known to the speaker (e.g., the girl).
dónde(
dohn
-
deh
)An adverb is a word that describes a verb, an adjective, or other adverbs (e.g., to run quickly, very tired).
a. where
¿Dónde quieren construir el edificio los arquitectos?Where do the architects want to build the building?
2. (colloquial) (in questions) (Latin America)
A word or phrase that is commonly used in conversational speech (e.g., skinny, grandma).
Regionalism used in Latin America: all the countries in South America, Central America, and the Caribbean. Does not include Spain.
a. how
¿Dónde iba a saber que cambiaste de opinión si no me lo dijiste?How was I to know that you'd changed your mind if you didn't tell me?