What exactly did you put on the SD card? Without knowing more about your level of expertise and which kobo you have, it's difficult to provide a useful answer.
Gen 1 kobo used uboot, wifi used redboot, and I don't own a touch, so I have no clue how it boots. If you're really up to playing with bootable embedded linux, the kobo GitHub should be a useful starting point for you.
https://github.com/kobolabs/Kobo-Reader
Doh, just re-read your OP. You said wifi so redboot. It's in the GitHub repo.