I'm glad to show you where to locate the check numbers when you reconcile a bank account, dr-valega.
The check number can be found under the Ref No. column on the Reconciliation page. If the field is empty, you need to open the check and put the number in the Ref No. field.
To do that, here are the steps you can follow.
Go to Accounting from the left menu, then Chart of Accounts.
Find and open the account that you want to reconcile.
Find the check and make sure to enter the check number in Ref No. field.
Click Save.
After entering the check number, go back to the Reconciliation page and continue reconciling your bank. I'm adding this article as your guide: