Can get access of consumers from merchant

[mianirfan3434]

Helo Community, 
I hope you will be good. I want to create an shopify app. but i want to know, which APIs or web hook will use. 

If merchant will install my app in their account. I want to get permissions from merchant to get merchant all subscribe customers/consumers. which shopify Api or webhook will use to get these information? 
Is there anyway to get customer/consumers data all details to proceed my app process? 

Thanks in advance.