You can add comments to text, objects, charts, table cells, and slides. When you don’t want comments to be visible, you can hide them. Comments are indicated with a square marker next to an object (text is also highlighted), and by a triangle in the corner of a table cell.
When multiple people are working on a presentation, each person’s comments appear in a unique color and include their author name. Anyone can reply to a comment, which is especially useful if you’re collaborating—you can add a comment, then with back-and-forth replies have a conversation in real time.
Note: Comments and highlights aren’t visible in printed presentations.
You can edit and delete your own comments and replies. If you’re the owner of the presentation, you can delete anyone’s comments, replies, or conversations.
Select text, or click an object or a table cell, then click 
in the toolbar.
Note: If you click the background of the slide (so that nothing is selected), you can add a comment to the slide that always stays open. You can resize the comment and reposition it on the slide. Others can’t reply to this type of comment.
Type your comment, then click Done (or click outside the comment).
To view, edit, or delete your comment, do one of the following:
Open a comment: Click the comment marker (or move the pointer over the highlighted text).
Edit a comment: If you’re the comment author, open the comment, click in the text, then type.
If there are replies to your comment, you can’t edit the original comment by clicking its text. Instead, move the pointer over the timestamp to the right of your name at the top of the comment. When the down arrow appears, click it, choose Edit Comment, then make your changes.
Delete a comment: If you’re the comment author or the presentation owner, click Delete at the bottom of the comment. If there are replies to the comment, this deletes the entire conversation.
If the comment is on the slide background, move the pointer over the comment, then click Delete.
Keynote > Preferences (from the Keynote menu at the top of your screen).
Click General.
Click the Text Size pop-up menu, then choose a size.
Click the comment marker (or move the pointer over the highlighted text).
Do any of the following:
Review a comment or conversation: Scroll through the text. If a comment is truncated, click Show More. If replies are hidden, click “View [n] more replies.”
Go to the next or previous comment (or highlight): Click the arrows at the bottom of a comment.
If the comment is on the slide background, move the pointer over the comment, then click the arrows.
Anyone you share the presentation with—by sending them a copy or inviting others to collaborate (with editing privileges)—can reply to a comment.
Click the comment marker (or move the pointer over the highlighted text).
Do any of the following:
Add a reply: Click Reply at the bottom of the comment, type your reply, then click Done. You can reply as many times as you like.
Edit your reply: Move the pointer over the timestamp (to the right of your name) for the reply you want to edit. When the down arrow appears, click it, then choose Edit Reply. Make your changes then click Done.
Delete your reply: If you’re the reply author or the presentation owner, move the pointer over the timestamp to the right of the name on the reply. When the down arrow appears, click it, then choose Delete Reply.
If you’re the owner of the presentation or author of the original comment in a conversation (a comment with one or more replies), you can delete the entire conversation.
Click the comment marker (or move the pointer over the highlighted text), then click Delete at the bottom of the conversation.
Do one of the following:
Click 
in the toolbar, then choose either Show Comments or Hide Comments.
Choose View > Comments > Show Comments or Hide Comments (from the View menu at the top of your screen).