How do you trade with a friend in Dragon Quest IX?

Answer 1

In order to trade with your friends, you both need to exchange your Nintendo 3DS' Friend Codes if you want to connect via internet or be next to each other. In both cases, the console's wireless switch must always be turned on.

Answer 2

Act as though to use an item, but select 'Transfer' instead of 'Use', and you can give the item to your friend (not if he/she is busy).