Can you use trading to build a wonder in 7 Wonders Duel?
Turns out this same questions has been asked on BGG.  Thankfully the designer Bruno Cathala has responded to this question clear "just to confirm: yes you can !".   

I can see from the question that a stretch it could be interpreted that Wonders are not buildings by wording of rules but the designer has clarified that trading is allowed for wonder construction.

BGG rules forum link.