wooassist

This plugin adds a custom field in the checkout page to ask your customers where they heard about your store.
This plugin also offers an “Other” field where your customer can provide a specific answer in a separate textbox.
Features:
<ul>
<li>Easily change the labels and choices for the custom field in the checkout page.</li>
<li>View reports on the “Reports” section in WooCommerce.</li>
<li>Enable/disable the custom field to be required on checkout.</li>
<li>Enable/disable the “Other” field.</li>
<li>Modify order statuses you want to include in the reports.</li>
<li>Export Orders with Customer Source field</li>
</ul>

Where Did You Hear About Us Checkout Field for WooCommerce

Adds a custom field in the checkout page to ask your customers where they've heard about your store.

pootlepress

nickburne

This plugin gives you lots of options for customizing the WooThemes Storefront theme for WooCommerce.
<h3>Usage</h3>
Install and activate the plugin. In your WordPress dashboard simply go to Appearance > Storefront Jetpack and there you will find various modules you can enable or disable for Storefront.

Storefront Jetpack

This plugin gives you lots of options for customizing the WooThemes Storefront theme for WooCommerce.

Where Did You Hear About Us Checkout Field for WooCommerce vs Storefront Jetpack