Comment Field

If you mean that you want to see the comments users have left in a property on the metadata card, you can use Compliance Kit's Managed Properties or Property Calculator for this.

Here's a sample rule for Managed Properties that copies the latest comment to the Latest comment property. Since comments are version-specific Managed Properties cannot keep all the comments in the property (the latest comment always overwrites the previous one).

With Property Calculator you can maintain the full comment feed. Here's a sample rule that also adds information on who left the comment and when (you can leave these details out if not relevant for your use case):

This is the result on the metadata card:

The way with the Compliance Kit works well but I dont know why, the PropertyCalculator Version doesent work...