macbook pro screen cracked, how to see the data

It is difficult to get an external display to work when you have issues with the built-in display. Make sure to force clamshell mode by closing the lid on the laptop. If it doesn't work the first time, then power off the laptop and make sure your external display is connected, then power the laptop back on and quickly close the display so the external display hopefully becomes the default one. You will need to use an external keyboard and mouse/trackpad.

As has been suggested by others, Target Disk Mode is a great option as well. Don't worry that you cannot see anything on the display. If Target Disk Mode has been activated, then you should be able to see the volume on another Mac. If you don't see the drive (perhaps because it is using Filevault), then launch Disk Utility to see if you can manually mount (unlock) the broken laptop's drive.

You may have better luck having an Apple Authorized Service Provider back up your data as they like to provide extra services above and beyond what Apple requires since Apple usually expects users to backup their own data. It is possible some Apple Stores may assist you anyway. It never hurts to ask.

Good luck.

Pull the disk, it that's possible, and get an external enclosure for it. If you have another Mac with matching ports, then connect them to use Target Disk Mode and try accessing the other computer's disk. Boot the one with the cracked screen into target disk mode. Boot the good Mac normally. You may find the disk on the cracked screen Mac on the Desktop of the good Mac. You can then access it like any other mounted disk.

You can help by telling us the model/year of your system.

Alternately, if you do not want to extract the drive (if you even can) or play with Target Mode from another Mac, you can call the Genius Bar to ask if they can extract the data to a drive you purchase (they have them available to buy in the Apple Store). Another poster said the Apple Store was willing to save the data before the system is sent off for screen replacement.

You can directly connect your MacBook to an external monitor, it should pick it up automatically,

The options for external screens are usually "Mirror Screens, Extended Screens, External Screen Only (also known as Clam shell mode)".

Depending on what model MacBook you have, you'll need a adapter, cable or both.

You can pick one up at Best Buy, the Apple Store or other name brand electronics store.

Here are the instructions:

https://support.apple.com/en-us/HT202351

Lets just hope the display ports are not damaged as well.

Good luck.