If i track an iphone using "Find my iphone" on another iphone , will it notify the location of the sign in and ask for the two-factor authentication code?

If it's a lost phone, why do want to avoid someone else seeing you track it?

If you have ever signed in to a web browser and checked the "remember me" button afterwards, you don't need the 2FA code there again.

Is this your Apple ID? Did you add a trusted phone number for use when your trusted device is not available?

IMO, if they are planning to keep the phone, it's not powered up. I would suggest alerting them is the least of your concerns. They should not be surprised you are trying to track the phone.

You had a chance to add another trusted phone number for this very situation.

When you set up 2FA you were given the opportunity to select more than one way of receiving the code. And you were also given a recovery key, with explicit instructions to save it and put it in a safe place, along with a reminder that by setting up 2FA you were taking total responsibility for your access to the account. Perhaps you forgot about the recovery key, but you should have it somewhere.

Yes

Sign into to iCloud and Find My iPhone will give you the location if it is online.

FYI... there is no longer a recovery key with 2FA. Password and trusted device/phone numbers only. On the plus side, there is an account recovery process.

You're correct; I was thinking of 2SV. but the recovery process should be usable.