"Where is the Esperanto congress?"
Translation:Kie estas la kongreso de Esperanto?
"la Esperanta kongreso" was one of the correct answers, along with "la kongreso de Esperanto," on 6/22/17. (This exercise was a multiple choice answer translating from English.)
Can someone explain to me the difference between Esperanto/Esperanta? Is Esperanta the adjective form?
Yes, in normal form, words ending in -o are nouns and words ending in -a are adjectives.