Can I write two cron( hook_cron() ) in one module I have a custom module abc_xyz and i want to write two seperate cron for this module. 

below is the code which i am trying but it is creating only one cron ,
with name abc_xyz_cron. it is not creating for zzz_yyy_cron

file name : abc_xyz.module

abc_xyz_cron(){

}

zzz_yyy_cron(){

}
No. You can implement hooks once per module due to the namespacing of the hook (mymodule_cron). However you can put conditions within the cron hook to do different things.

You might be looking for this instead: https://api.drupal.org/api/drupal/modules!system!system.api.php/function/hook_cron_queue_info/7.x