Can someone please tell me what it is meant when the Major quest asks me to "vend 29 times"? Thank you.

It means you go to a vending machine (there's one in every land) and vend from it that many times. You need wizard tokens to do so, which you can buy from user shops or get by doing Wizard Quests.

Okay thanks very much for the info :) Looks like I'll have to skip that one too since I don't have any tokens.