I need to print a check and it's not showing.

Hi @cigarr , thank you joining quickbooks community. 

How to print cheques in QuickBooks Online

1. Select + New.
2. Select Print Cheques.
3. Load your cheques into the printer.
4. Select the bank account containing the cheques you wrote that need to be printed.
5. In the Starting cheque no. field, enter the cheque number of the first cheque in the printer. The cheque number is found to the right of the account number at the bottom of the cheque.
6. Select Preview and print. If everything is correct, select Print.
7. If your cheques printed OK, select Done.

Article How to print checks 

You could edit it, save it, edit again, re enter to print. Let community on your back for every assistance. Cheers.