Bonnet release cable snapped at catch under bonnet. How do I lift bonnet?

SOURCE: Bonnet latch will not open and bonnet is in closed position

the cable connecting the handle to the latch is broken. remove the front grille and access the latch assembly. you will be able to release by hand and then replace the cable.

SOURCE: Bonnet cable routing Mitsubishi Evo VI

Your cable is generally sold as a one piece unit...cable inside housing. (same as a bicycle brake cable) Many even come with the release handle attached. Therefore, you simply feed the new one in exactly where the old one went and attach it to the lock mechanism. This can easily be done by attaching a wire to the latch end of the old unit and pulling it out from the drivers compartment, then attaching the new one to the wire and pulling it back through. In that way, you don't need to see it to install it (like snaking a wire through a finished wall, without opening the wall.)
If you do it carefully, it should not be that difficult.
Good Luck!!