To get the list of topics that has under replicated paritiions, use the following command:
kafka-topics.sh --bootstrap-server <broker> --describe | \
awk '/Topic:/ && /Partition:/ && /Isr:/ {
n=split($0,a,"Replicas: "); split(a[2],b," "); r=split(b[1],_,",");
n=split($0,a,"Isr: "); split(a[2],b," "); i=split(b[1],_,",");
if (r != i) print $2
}' | sort | uniq
To describe the topic use: