What is ex date record for any scrip for divident or buyback?

What is ex date for any scrip for record purpose is T+1 OR T+2 . Please clarify , so accordingly we may trade for any share

To be eligible for any Corporate Action (Dividends, Buyback, Bonus etc.) you need to buy shares before ex-date.

If record date is tomorow (21.8.20, can I buy it today(20.8.20) ?

As I said above, if you want to stand eligible for Corporate Actions, you will have to buy the stock before the ex-date, you won’t be eligible if you buy on ex-date. Ex-date always comes before Record Date.

Still my que is if i buy today , tomorrow is ex date for MCX , T+1 will be counted or not?

Settlement will happen on T+2 days only, but since you are buying before ex-date, you will be eligible for Dividends.

The money for buyback is deposited in trading account or come directly to bank account? I had received the CN for justdial buyback but yet to see the money.

This is credited to your primary bank account.