If you have an ansible group called zookeeper_hosts, you can simply use:

hosts: zookeeper_hosts
  sudo: yes
  roles:
    - role: sujaymansingh2.zookeeper
      zookeeper_servers: '{{ groups["zookeeper_hosts"] }}'

Make sure that each host has a zookeeper_myid attribute. I usually do this by adding an attribute in the hosts file.

[zookeeper_hosts]
zookeeper-1.example.com zookeeper_myid=1
zookeeper-2.example.com zookeeper_myid=2
zookeeper-3.example.com zookeeper_myid=3