How to I get information to print on the memo line of a check? I do already add it when creating the check, but it doesn't print it

The check's Print Setup includes two types: Voucher and Standard. Both types allow the Memo to appear when printing checks, Tishie18.

You can take a look at these screenshots for comparison.
 

If you are referring to the Description line on the check, please note that it only displays in the Voucher check setup.
 

Here’s an article to guide us in configuring and troubleshooting the check Print Setup in QuickBooks Online: Configure and troubleshoot your print settings for printing checks in QuickBooks Online.
 

Feel free to reach out if you have any other questions or need further assistance.