Here are the steps to duplication items in MCPE, you will need two player or more to do this.

1: make a chest

2: put the item or items in the chest that you want to duplicate

3: have the 2 players or more go in the chest and tap the item at the same time

This also works if there is more than one item you tap and hold the item at the same time

I hope this was helpful to you!

By: LoLo the EPIC