You can not just move a question to the top because the questions are sorted in a predefined order. What you can do is to modify the question so that it gets to the top of that predefined order.
That order is usually the date it was asked (for example, for the Questions page). However, for the All Activity page this order is based on the last modification to the question, where modification means question edit, comment post/edit, answer post/edit, etc.
So the short answer is you can't change the order in the Questions page because it is sorted based on the asked date, which is fixed. But you can just edit the question and that update would bring it to the top of the All Activity.
If you don't want to perform a "fake edit" on a question to bring it to the top of the All Activity section then you can consider this plugin http://www.question2answer.org/qa/31264 ... which I think I started developping after seeing this post back in January :)
Finally, and covering all scenarios, you could also perform some core hacks or use plugin overrides to change this behaviour but I wouldn't advise it.
