We can add a custom field, chanscar.

This way, it will display the check number when printing the Sales Receipt. Let me guide you with these steps:

1. From the Gear icon, select Custom form styles.
2. In the New style drop-down, select Sales receipt.
3. Go to the Content tab.
4. Click the pencil (edit) icon on the header section.
5. Go to the Custom fields section and then click Manage custom fields.
6. Click Add field.
7. Select whether it's Customer info, Vendor info, or Transaction info.
8. You can enter Check Number as the field Name.
9. In the Type section, select Number.
10. Tick the Use on sales form and Show to customer boxes.
11. Click Save.

Afterward, you're good to create a Sales receipt and then enter the check number.

 You can take a look at these articles when customizing a sales receipt:

• Add a discount to an invoice or sales receipt
• Customize invoices, estimates, and sales receipts in QuickBooks Online

There you have it, chanscar. Let me know if you still have other concerns. Stay safe!