Dock allows you to comment on any section in a Workspace. To do so, start by navigating to the Workspace in question and make sure you're on the "Shared" view!

Step 1: Navigate to the desired section and roll over it with your mouse or select it.

Step 2: Click on the comment icon to Start new comment thread:

Step 3: Type comment or tag people by using the "@" symbol. Anyone you tag will receive an email notification.

If they've been in the space before, they should be listed as an option by name. Otherwise you can @ an entire email address.