How do I get a keyboard on my Apple Watch Series 7?

If you see this screen on your watch when trying to type:

Tap on the scribble icon in the right corner to get back to the icons for all input options:

After that tap on the keyboard icon to bring up the keyboard.

And the watch should remember your input method for the next time.

You may consider reading the details from the below link from Apple

Enter text on Apple Watch

A small excerpt from above link

But to read the article for additional details

" You can enter text by dictating, scribbling with your finger, or typing on the onscreen keyboard. You can also use emoji and switch to typing on your paired iPhone. "