After you read and reply to a question, there is no way to distinguish between the read and unread questions unless you move a question from the New column to the Accepted column.
We recommend all questions to which you've responded, or are otherwise finished, be marked as Accepted.
Access the Q&A Moderation page.
Check the message(s) you've read.
Click Mark as Accepted. The message disappears from the New category and appears in the Accepted category.
Questions can be moved back to the New category by checking the message(s) and clicking Mark as New.