In a Google Doc type a colon either at the start of a line or anywhere after a space, and the emoji search box will drop down, like this:

GIF demonstrating where to place the colon in order to see the emoji search drop down.

Then, type in words to search for your emoji, like this:

Fun, right?! 👍 🥳 🙌 😎 🤩

 

Want to know how I made those GIFs? Watch this tutorial and/or read this post.