How do I access “search” on my iPad?

To expose the search dialogue, you’ll need to swipe downwards from any empty area of the screen - other than the top or extreme corners of the screen.

Swiping downwards from the top edge will open the Notifications screen.

The best way is for you to drag down from the top of the screen, you can access it this way or if you have a keyboard attached CMD+Space can activate search too.