Can I obtain the date on which a contact has subscribed to email marketing?

You can do this with the help of Workflows' Update Fields action.

• First, create a custom field called Subscription Date from Settings > Module Management > Module Layouts & Fields.
• Then follow these steps to set up the Update Fields action:

1. Select the Contacts module under Basic Information.
2. Set the Entry Criteria to Email Opt-in has changed to Double Opt-in.
3. Create an Update Fields action to update the Subscription Date to the current date.

So, the day on which the Email Opt-in field changes to Double Opt-in is updated in Subscription Date.
To learn more about the Update Fields action, click here.