A memrise user-made lesson I’m doing says that ここ translates to “where”, along with “どこ”, but looking in a dictionary, it says that only “どこ” means “where.” Anyone know anything about this, as well as how trustworthy memrise user-made lessons tend to be?
ここ means “here”. Sounds like you probably shouldn’t trust that user’s lessons anymore. 
He may have just made a typo, to be honest. “Where” is just 1 letter from “here”.
Unless the lesson kept saying it meant where, in which case that’s a problem…
Nevermind, I realized the problem. He said that “koko, doko” means “where am I”, but the comma wasn’t indicating two separate words for the same thing, it was referring to a normal comma in a phrase. The guy meant that “koko, doko” is a phrase that means “where am I”, literally translating to “here, where.” Do you know if that is what that phrase means?
It does mean that, though it’s very casual.
It does mean that, but keep in mind this is very colloquial because it doesn’t include particles. To say it more “correctly” (from a grammar perspective) you would say “ここはどこ？”. The は marks ここ as the topic. It could awkwardly be translated as “as for here, where (is it)?”. You should avoid omitting particles until you’re more familiar with the language so you don’t form bad habits.