I believe there is combination of attack + def or str + hp
you get 35k xp in 2 skills you choose and 20k in skills you don't choose
what i'm asking is, is it possible to get xp in selected skills but not the other ones
Both incorrect.
When you choose your XP reward you do have a choice between strength & constitution or defense & attack, BUT the selection you make doesn't eliminate the other two - it just pushes the majority of XP towards your choice (you still receive experience in the other two, just not as much). Unfortunately this is unavoidable
Bear in mind, you NO LONGER have to accept the experience to complete the quest - and you are allowed to return to crash island and Ape Atoll as well as talk to Daero without going through the training. This was an addition a while ago allowing pures to complete Monkey Madness without ruining them, and also providing them with the opportunity to gain Adamant gloves instead of the maximum which used to be just Mithril.