Define Snapshot

Point in time backup for EBS volume.

Are snapshots regional ? Justify.

yes

If a volume is encrypted, will the snapshot taken will also be encrypted or do we need to encrypt is separately ?

An encrypted EBS volume always produces an encrypted snapshot

Is it possible to copy a snapshot from one region to another ?

yes

Can we directly attach the snapshot taken to another EC2 instance or is there any other step involved ?

you cannot directly attach an EBS snapshot to an EC2 instance