Assuming you are talking about dialogue in a novel or short story and not a screenplay, then you are well to be concerned that gimmicks depending on punctuation can result in readers not interpreting your dialogue as you intended.
It is best to avoid complicated punctuation to convey specific meanings since they lead to individualistic interpretations.
Everybody interprets non-standard punctuation differently. To me, in dialogue, an em-dash indicates a long pause. To others, it might read like a parenthetical outburst. That is why things like dashes and ellipsis are best to be kept to a minimum.
If there is a very specific behavior you want to communicate -- something that is important for the moment or to characterization -- then action beats are terrific. They magnify the dialogue through the use of gesture or bodily action, deepening the characterization. Making them more imaginable, therefore more immersive.
If what you are wanting to convey in the story isn't very important -- as in it needs to be there but doesn't warrant too much ink, then use parenthesis for the second em-dash. That could convey that the character is kind of spouting off about their career options at some future time. The upside of this approach is it will look reasonably professional since it extends itself to a narrow range of interpretations. In the end, it doesn't matter until someone publishes the story, in which case an editor will be involved and they'll make recommendations based on their interpretations of the scene.
