You'll need to know how much travel you had, and try to get a fork with the same amount (20 mm more or less won't make a huge difference.)
You will also need to know the steerer tube overall length. Many used Ebay forks have the tube cut to fit their bike - and it may not fit yours. Too long is OK - you can cut to fit. Too short is too short.
Make sure the fork you get is able to fit V-brakes, as I assume your bike had. Some forks are disc brake only and have no mounting bosses for V-brakes.