Why not "Apakah tujuan mereka?"
"apakah" should be okay as well.
Tujuan mereka apa? - would this also work?
Yes, that should also work.
Thanks! Just want to say that I've seen a lot of your comments in this Indonesian course and I have always found them useful and helpful. Keep up the good work! :)
Why noy "Apa yang tujuan mereka"?