Edit /etc/fstab file. You will find screen something like below:
LABEL=/home /home ext3 defaults,usrquota,grpquota 1
You can see usrquota,grpquota lines in /home partition that means quota is enabled for user accounts and group for the partition /home.
If the quotas are not enabled then you can enable it via following below steps.
1. Enable quotas per file system by modifying /etc/fstab
2. Remount the file system(s)
3. Create the quota files and generate the disk usage table
4. Assign quotas