The cargo ship is .......... at the harbour to unload the goods.

I think the word they are looking for is docked.

My doubt is that they use the word "at" which suggests that there should be a proper noun to follow. Eg. "The cargo ship is docked at Singapore harbour to unload the goods." I thought it should say "The cargo ship is docked in the the harbour to unload the goods" since it does not follow with a proper noun.

This is my thought anyway. I am not the best in English so best to listen to others too