How to generate Trial Balance report monthly with 1) opening balance,2) Dr & Cr for the month 3) Closing Balances?

You'll want to run the General Ledger report, usera-lee.

A Trial Balance report is a summary of debit and credit balances of the accounts on your Chart of Accounts in a specified period. Information such as the opening or closing balances of such accounts are unavailable for this report. You can pull up the General Ledger report, which has the information you need.

Let me show you how: 

1. Go to the Reports menu. 
2. Enter and select in the search field, General Ledger.
3. At the upper-right, click Customize.
4. Select the Report period (Month).
5. Under the Rows/Columns option, select Change columns. 
6. Select Debit, Credit, and Open Balance.
7. Click Run report. 

For more details in customizing your reports, you can see here: Customise reports in QuickBooks Online.

Keep me posted if there's anything else that you need help with. Take care and have a great day!