Hi Santosh!
We do have some v1 information for retrieving subscribers to boards here:
https://community.lithium.com/t5/Developer-Documentation/bd-p/dev-doc-portal?section=commv1&leaf-id=Board.subscriptions#Board.subscriptions
For v2, we have documentation on calls you can use here:
https://community.lithium.com/t5/Developer-Documentation/bd-p/dev-doc-portal?section=commv2&collection=subscriptions
Examples:
SELECT id, target FROM subscriptions WHERE subscriber.id = '3456'
SELECT id, target FROM subscriptions WHERE node.id = 'boards:cellphones'
Hope this helps!
Cheers,
Maureen