How do i mirror my macbook with a broken screen?

Try using just T for target disk mode…

Use target disk mode to share files between two Mac computers - Apple Support

How is it connected to the iMac?

I think the disk should connect with 'enter password to mount' dialog.

Depending on the model you could contemplate removing the HD & fitting another - Apple can't wipe it if you don't give it to them 🙂

Look for the manual on Apple.com or use ifixit.com there are often guides for user replaceable parts. I'd link to Apple manual if they had a search system that worked… http://manuals.info.apple.com/ <- good luck with that 🙂

Hi,

If you're trying to connect to another Mac in Target Disk Mode (Use target disk mode to share files between two Mac computers - Apple Support) hold down just the T key, not Shift T. I've never tried Shift T, so I don't know what will happen and if that's what's preventing you from entering Target Disk Mode, or if there's more wrong with your Mac than the display.

I've also tried plugging it into the iMac and pressed Shift T

It's just the "T" key, not, "Shift-T."

"Command-F1," should turn on an external display as a mirror.

Also, see: https://apple.stackexchange.com/questions/82224/macbook-pro-screen-has-died-want ing-to-use-secondary-display