If I understand correctly what you mean, you have to work with variables. You can define variables (e.g. Book or Talked - whatever you like to name it) and changing the settings in the hotspot properties:
e.g. to a variable to get the value 1 when clicked on it
or to make hotspots appear only if another hotspot was clicked and has already a value of 1.
If you want that the person and the book/key appear on the same screen/ in the same room, you will probably need to make 2 identical screens, but only on the second screen make a clickable hotspot.
So on the first screen the player clicks e.g. a book (you can set then the value for "Book" to 1 if necessary for other purposes aswell, and set it to go to the next identical screen).
On the second screen the other hotspot appears and becomes clickable, or the conversation starts.
Hope that was half way clear, if you have any questions or need more details, don't hesitate to ask.
You can find great help in the help files on how to use variables, even with two examples:
http://www.adventuremaker.com/help/puzzles.htm