Does QBO auto generate transaction number? If not which report can capture all transactions with serial no.?

Let me provide some information about the transaction number, @qbo10.

QuickBooks Online will automatically assign a transaction number to your sales transactions. For the expense and other related transaction types, you'll have to enter it manually in the Ref no. or No. field.

It will also reflect when you pull up the Transaction Detail by Account report. Let's make sure to check the Num column that you can find on the Gear icon.

Here's how: 

1. Sign in to your QuickBooks Online account.
2. From the left menu, choose Reports.
3. In the Find report by name field, search for Transaction Detail by Account.
4. Go to the Gear icon and tick the Num box.
   

Additionally, you have the option to personalize your reports. You can check this reference for the detailed steps: Customise reports in QuickBooks Online.

Please reply again if you need more help. I'll be glad to lend a helping hand. Wishing you all the best.