If customers signing up for recurring payments for a regular subscription service is what you're looking for, this support info might be helpful - https://squareup.com/help/us/en/article/6839-subscription-payments-with-square-online-checkout-links
If you're looking for folks that have given the 'ok' to recieve marketing content from you is what you're looking for:
Click the Hamburger menu to open the left navigation pane > Click CUSTOMERS > Choose CUSTOMERS (yes again) > from here, you can filter how you'd like to see your customer list.
Some good info and much more broad look at customer email collection - https://squareup.com/help/us/en/article/5976-get-started-with-email-collection-tools
For Loyalty customers, follow the same process, chosse LOYALTY instead of Customers (the second time).
Some good info on Loyalty - https://squareup.com/help/us/en/article/6465-square-loyalty-get-started-guide
Take care of yourself and, as life provides, someone else too.
