when i connect my iPhone to MacBook, I cannot locate the pop-up screen "Trust this computer" on my iPhone, what can i do?

Once you have trusted a device, you need not trust every time you connect.

Connect iPhone to Mac

Use your USB lightening cable --> Resolve USB-related alerts in iTunes - Apple Support

If unable to connect --> If iTunes doesn't recognize your iPhone, iPad, or iPod - Apple Support

For your Mac --> If your computer doesn't recognize your iPhone, iPad, or iPod ...

Use genuine cable --> Identify counterfeit or uncertified Lightning connector accessories ...

See how to --> Sync your iPhone, iPad, or iPod using iTunes on your computer ...

If you are experiencing an issue not listed here, contact support