Translation:The journalist works at a local channel.
I'm not very knowledgeable about how "channels are assigned". this sentence as you can see was created some time ago and we have no way of knowing what the original concept was meant to be. Please give us some idea of how to write a better sentence using this vocabulary so we can avoid errors in the future.
I agree - 'on' is better than 'at'. but is marked wrong: https://screenshots.firefox.com/Cv1acT88a5vxQy51/www.duolingo.com