There's topic with 22 replicas, 50 partitions and 22 running Kafka brokers.
Topic manual assignment screen in Kafka Manager shows that there's Broker Down in all topic partitions as seen in the image.
How to determine Kafka broker that's down using cli or Kafka Manager?
Currently, i look which broker id is missing in Partition replicas.

This information on brokers is also maintained in Zookeeper. So, you could go onto one of the zookeeper nodes and use the cli to extract this and here's a command sequence you could use:
zookeeper-clientand this should invoke the zookeeper command promptls /brokers/idsand this should return the ids of all the active brokers