so, if you wanted to evolve a pokemon holding a item whilst trading and you wanted the evolved form heres what to do.....
1.fly/walk to Jubilife City
2.Go to the GTS
3.Deposit the pokemon you want to evolve with the item and trade it for a impossible offer
Dialga lv.9 and under
palkia lv.9 and under
4.Trade with another pokemon
5.Look at the summary and leave as is
6.walk out and straight back in the GTS
7.look at summary and take back your pokemon
and there you go
1.fly/walk to Jubilife City
2.Go to the GTS
3.Deposit the pokemon you want to evolve with the item and trade it for a impossible offer
Dialga lv.9 and under
palkia lv.9 and under
4.Trade with another pokemon
5.Look at the summary and leave as is
6.walk out and straight back in the GTS
7.look at summary and take back your pokemon
and there you go