Do you mean the one that shows up when you're typing and want to go back in the text to edit? You place your finger on the text for editing, the cursor will move there and a magnified area will show up allowing you to adjust the position of the cursor. You have to hold your finger on the text for the circle to show up.
Another one that I use is the three finger double tap and the screen zooms in. The setting and instructions are in the Settings app under General, Accessibility, then Zoom. You can make the screen zoom in a lot to see the fine print, or other details.
Sent from my iPad using iPF - Peace