I have launched an ec2 RHEL instance and have attached EBS volume to it.
How do I know when I access data from /tmp or /opt or any other directory, whether the data is accessed from Instance Store or EBS?
The t2.medium instance type (mentioned in comments) does not include instance store volumes. You can review all instance types with instance store volumes here. In addition when launching instances with instance store volumes these aren't your root volume and are just available storage you can mount as an additional disk on the instance. For example if you launch a M5d.large instance, by default your instance store NVMe drive is available at /dev/nvme1n1 in linux, but is not used at launch time. You can format and use the instance store volume as you please, after launch.