If you'd like to add emojis to the text you're typing on the whiteboard, you can do that in different ways.
While selecting the TEXT tool and setting the cursor in the text box, you can either:
Copy and paste an emoji from any page, such as this one.
If you work on a Mac, press Command+Control+Space to open the Emoji keyboard and double click on the one you'd like to add.
If you work on Windows, press Win+Period to open the Emoji keyboard and click on the one you'd like to add.