What will you do?When you grow up?in the future

加在两个问句中任意一个都可以
what will you do in the future when you grow up?
what will you do when you grow in the future?
表达的意思都是一样的

放在中间和最后都可以 即：
What will u do in the future when u grow up?
What wiil you do when u grow up in in the future.

其实貌似不用加in the future了，有点累赘了
What will you do When you grow up?或What will you do in the future？

When you grow up in the future

加在When you grow up的后面

前面。